ART: Do not use std::<container>::at().

These functions are specified as throwing std::out_of_range
and we do not use exceptions.

Test: m
Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Change-Id: I67c365ed6d779c101a18b9f386c751c48ca76e16
diff --git a/compiler/utils/mips/assembler_mips.cc b/compiler/utils/mips/assembler_mips.cc
index dce5b95..c0b6f98 100644
--- a/compiler/utils/mips/assembler_mips.cc
+++ b/compiler/utils/mips/assembler_mips.cc
@@ -4801,10 +4801,9 @@
 
   // Write out entry spills.
   int32_t offset = frame_size + kFramePointerSize;
-  for (size_t i = 0; i < entry_spills.size(); ++i) {
-    MipsManagedRegister reg = entry_spills.at(i).AsMips();
+  for (const ManagedRegisterSpill& spill : entry_spills) {
+    MipsManagedRegister reg = spill.AsMips();
     if (reg.IsNoRegister()) {
-      ManagedRegisterSpill spill = entry_spills.at(i);
       offset += spill.getSize();
     } else if (reg.IsCoreRegister()) {
       StoreToOffset(kStoreWord, reg.AsCoreRegister(), SP, offset);