Fix build: Don't compare unsigned int with signed int.

Change-Id: Iad3d2a9aa30c647a3b847b162a1692287dad83e9
diff --git a/src/oat_file.cc b/src/oat_file.cc
index 7762825..e97e70c 100644
--- a/src/oat_file.cc
+++ b/src/oat_file.cc
@@ -188,7 +188,7 @@
 
 #else
   oat = map->Begin() + oat_header.GetElfImageTableOffset();
-  CHECK_EQ((reinterpret_cast<uintptr_t>(oat) & 0x3), 0);
+  CHECK_EQ((reinterpret_cast<uintptr_t>(oat) & 0x3), 0u);
 
   for (uint32_t i = 0, end = oat_header.GetElfImageCount(); i < end; ++i) {
     uint32_t elf_offset = *reinterpret_cast<const uint32_t*>(oat);