ART: Fix old warnings

Fix Wconstant-conversion warnings.

Partially reverts commit df53be273509dd43725870fb20a2c7d71f7fbfd3.

Bug: 28149048
Bug: 29823425
Test: m
Test: m test-art-host
Change-Id: Ib377150690c0f2c2142e4b91f2144e2bcaa020ef
diff --git a/compiler/utils/mips/assembler_mips_test.cc b/compiler/utils/mips/assembler_mips_test.cc
index c24e1b1..0917530 100644
--- a/compiler/utils/mips/assembler_mips_test.cc
+++ b/compiler/utils/mips/assembler_mips_test.cc
@@ -2851,7 +2851,7 @@
   // Account for 5 extra instructions: ori, addu, lw, jalr, addiu.
   uint32_t offset_forward = (kAdduCount1 + 5) * sizeof(uint32_t);
   // Account for 5 extra instructions: subu, addiu, sw, nal, lui.
-  uint32_t offset_back = -(kAdduCount1 + 5) * sizeof(uint32_t);
+  uint32_t offset_back = static_cast<uint32_t>(-(kAdduCount1 + 5) * sizeof(uint32_t));
 
   std::ostringstream oss;
   oss <<