MIPS: Fix debug mode test failures.

This commit fixes a couple of debug mode test failures,
which were introduced by commit 14600.

TEST=mjsunit/mirror-number,mjsunit/mirror-object

BUG=

Review URL: https://codereview.chromium.org/15179005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14699 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/stub-cache-mips.cc

@@ -621,7 +621,6 @@ void StubCompiler::GenerateStoreTransition(MacroAssembler* masm,
       } else {
         ASSERT(storage_reg.is(name_reg));
       }
-      __ mov(name_reg, value_reg);
       __ RecordWriteField(scratch1,
                           offset,
                           name_reg,