aom_dsp/x86/blend_a64_mask_sse4: fix int sanitizer warnings

implicit conversion from type 'int' of value 255 (32-bit, signed) to
type 'char' changed the value to -1 (8-bit, signed)

BUG=aomedia:2357

Change-Id: I64b2f7e615095b62dec575d4ddf8422880edafe6
diff --git a/aom_dsp/x86/blend_a64_mask_sse4.c b/aom_dsp/x86/blend_a64_mask_sse4.c
index 22c304e..a9b47af 100644
--- a/aom_dsp/x86/blend_a64_mask_sse4.c
+++ b/aom_dsp/x86/blend_a64_mask_sse4.c
@@ -339,8 +339,8 @@
     uint8_t *dst, uint32_t dst_stride, const uint8_t *src0,
     uint32_t src0_stride, const uint8_t *src1, uint32_t src1_stride,
     const uint8_t *mask, uint32_t mask_stride, int w, int h) {
-  const __m128i v_zmask_b = _mm_set_epi8(0, 0xff, 0, 0xff, 0, 0xff, 0, 0xff, 0,
-                                         0xff, 0, 0xff, 0, 0xff, 0, 0xff);
+  const __m128i v_zmask_b =
+      _mm_set_epi8(0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1);
   const __m128i v_maxval_b = _mm_set1_epi8(AOM_BLEND_A64_MAX_ALPHA);
   const __m128i _r = _mm_set1_epi16(1 << (15 - AOM_BLEND_A64_ROUND_BITS));
   do {
@@ -518,8 +518,8 @@
     uint16_t *dst, uint32_t dst_stride, const uint16_t *src0,
     uint32_t src0_stride, const uint16_t *src1, uint32_t src1_stride,
     const uint8_t *mask, uint32_t mask_stride, int h, blend_unit_fn blend) {
-  const __m128i v_zmask_b = _mm_set_epi8(0, 0xff, 0, 0xff, 0, 0xff, 0, 0xff, 0,
-                                         0xff, 0, 0xff, 0, 0xff, 0, 0xff);
+  const __m128i v_zmask_b =
+      _mm_set_epi8(0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1);
   const __m128i v_maxval_w = _mm_set1_epi16(AOM_BLEND_A64_MAX_ALPHA);
 
   do {
@@ -565,8 +565,8 @@
     uint32_t src0_stride, const uint16_t *src1, uint32_t src1_stride,
     const uint8_t *mask, uint32_t mask_stride, int w, int h,
     blend_unit_fn blend) {
-  const __m128i v_zmask_b = _mm_set_epi8(0, 0xff, 0, 0xff, 0, 0xff, 0, 0xff, 0,
-                                         0xff, 0, 0xff, 0, 0xff, 0, 0xff);
+  const __m128i v_zmask_b =
+      _mm_set_epi8(0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1);
   const __m128i v_maxval_w = _mm_set1_epi16(AOM_BLEND_A64_MAX_ALPHA);
 
   do {
@@ -710,8 +710,8 @@
     uint16_t *dst, uint32_t dst_stride, const uint16_t *src0,
     uint32_t src0_stride, const uint16_t *src1, uint32_t src1_stride,
     const uint8_t *mask, uint32_t mask_stride, int h, blend_unit_fn blend) {
-  const __m128i v_zmask_b = _mm_set_epi8(0, 0xff, 0, 0xff, 0, 0xff, 0, 0xff, 0,
-                                         0xff, 0, 0xff, 0, 0xff, 0, 0xff);
+  const __m128i v_zmask_b =
+      _mm_set_epi8(0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1);
   const __m128i v_maxval_w = _mm_set1_epi16(AOM_BLEND_A64_MAX_ALPHA);
 
   do {
@@ -762,8 +762,8 @@
     uint32_t src0_stride, const uint16_t *src1, uint32_t src1_stride,
     const uint8_t *mask, uint32_t mask_stride, int w, int h,
     blend_unit_fn blend) {
-  const __m128i v_zmask_b = _mm_set_epi8(0, 0xff, 0, 0xff, 0, 0xff, 0, 0xff, 0,
-                                         0xff, 0, 0xff, 0, 0xff, 0, 0xff);
+  const __m128i v_zmask_b =
+      _mm_set_epi8(0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1, 0, -1);
   const __m128i v_maxval_w = _mm_set1_epi16(AOM_BLEND_A64_MAX_ALPHA);
 
   do {