SoftAVCEncoder: fix mismatched type for comparison.

Bug: 20674674
Change-Id: Iace5b8c882339b3a9d2e706375255aeeeb0532fe
diff --git a/media/libstagefright/codecs/avc/enc/SoftAVCEncoder.cpp b/media/libstagefright/codecs/avc/enc/SoftAVCEncoder.cpp
index 523e785..e3fdc89 100644
--- a/media/libstagefright/codecs/avc/enc/SoftAVCEncoder.cpp
+++ b/media/libstagefright/codecs/avc/enc/SoftAVCEncoder.cpp
@@ -259,7 +259,7 @@
     int32_t nMacroBlocks = ((((mVideoWidth + 15) >> 4) << 4) *
             (((mVideoHeight + 15) >> 4) << 4)) >> 8;
     CHECK(mSliceGroup == NULL);
-    if (nMacroBlocks > SIZE_MAX / sizeof(uint32_t)) {
+    if ((size_t)nMacroBlocks > SIZE_MAX / sizeof(uint32_t)) {
         ALOGE("requested memory size is too big.");
         return OMX_ErrorUndefined;
     }