MIPS: Fix ARM bug introduced in r12604 that caused crashes on ARM on crypto-md5 from SunSpider.

src/mips/macro-assembler-mips.h

Index: src/mips/macro-assembler-mips.h
diff --git a/src/mips/macro-assembler-mips.h b/src/mips/macro-assembler-mips.h
index ad3004aa67bafd8729f113ea7cdb6add366267cb..a13c8ecf2da48516be2ad6b2ddbcb8268885e0cc 100644
--- a/src/mips/macro-assembler-mips.h
+++ b/src/mips/macro-assembler-mips.h
@@ -973,6 +973,7 @@ class MacroAssembler: public Assembler {
   void StoreNumberToDoubleElements(Register value_reg,
                                    Register key_reg,
                                    Register receiver_reg,
+                                   // All regs below here overwritten.
                                    Register elements_reg,
                                    Register scratch1,
                                    Register scratch2,