MIPS: Fix mistake in r12549 (1597d7d9).

This commit fixes several test failures introduced by r12549 (1597d7d9):
- mjsunit/regress/regress-760-1
- mjsunit/strict-mode
- mjsunit/string-add

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/11039014
Patch from Akos Palfi <palfia@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12647 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/full-codegen-mips.cc

@@ -2719,7 +2719,7 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   STATIC_ASSERT(kSmiTagSize == 1);
   STATIC_ASSERT(kPointerSize == 4);
   __ li(at, Operand(DescriptorArray::kDescriptorSize));
-  __ Mult(a3, at);
+  __ Mul(a3, a3, at);
   // Calculate location of the first key name.
   __ Addu(t0, t0, Operand(DescriptorArray::kFirstOffset - kHeapObjectTag));
   // Calculate the end of the descriptor array.