MIPS: Move failing ASSERT to a more sane place.

Port r19095 (caf48ad)

Original commit message:
Objects can actually be stored into themselves. This fails when no write
barrier is needed (eg, the object was just allocated).

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/149343003

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19122 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/mips/lithium-codegen-mips.cc

@@ -4001,7 +4001,6 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
 
   // Do the store.
   Register value = ToRegister(instr->value());
-  ASSERT(!object.is(value));
   SmiCheck check_needed =
       instr->hydrogen()->value()->IsHeapObject()
           ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;