Fix building mkdtimg against musl

Fix building mkdtimg against musl libc by fixing a -Wformat error
that is not caught by glibc because glibc's fprintf is not annotated
with the __printf__ attribute:
system/libufdt/utils/src/mkdtimg_dump.c:92:21: error: flag '+' results in undefined behavior with 's' conversion specifier [-Werror,-Wformat]
  fprintf(out_fp, "%+20s = %d\n", name, fdt32_to_cpu(value));

Bug: 190084016
Test: m USE_HOST_MUSL=true mkdtimg
Change-Id: Ibcb5a8839cc3c220789927a7eeffce162fb21613
diff --git a/utils/src/mkdtimg_dump.c b/utils/src/mkdtimg_dump.c
index 5ca2eb8..b28e3cf 100644
--- a/utils/src/mkdtimg_dump.c
+++ b/utils/src/mkdtimg_dump.c
@@ -89,19 +89,19 @@
 
 
 static void output_prop_int(FILE *out_fp, const char *name, uint32_t value) {
-  fprintf(out_fp, "%+20s = %d\n", name, fdt32_to_cpu(value));
+  fprintf(out_fp, "%20s = %d\n", name, fdt32_to_cpu(value));
 }
 
 static void output_prop_int_cpu(FILE *out_fp, const char *name, uint32_t value) {
-  fprintf(out_fp, "%+20s = %d\n", name, value);
+  fprintf(out_fp, "%20s = %d\n", name, value);
 }
 
 static void output_prop_hex(FILE *out_fp, const char *name, uint32_t value) {
-  fprintf(out_fp, "%+20s = %08x\n", name, fdt32_to_cpu(value));
+  fprintf(out_fp, "%20s = %08x\n", name, fdt32_to_cpu(value));
 }
 
 static void output_prop_str(FILE *out_fp, const char *name, const char *value) {
-  fprintf(out_fp, "%+20s = %s\n", name, value);
+  fprintf(out_fp, "%20s = %s\n", name, value);
 }
 
 static void output_table_header(FILE *out_fp, const struct dt_table_header *header) {