MIPS: Fix `[date] Migrate Date field accessors to native builtins.'

Port fc5c7e04

Original commit message:
There's no reason to have JavaScript wrappers for those accessors,
since the meat is already in hand-written native code (via %_DateField).
First step now to put them into native builtins. Next step will be to
completely remove %_DateField.

BUG=
TEST=test262/built-ins/Date/prototype/toISOString/15.9.5.43-0-10, test262/built-ins/Date/prototype/toISOString/15.9.5.43-0-11, test262/built-ins/Date/S15.9.3.1_A5_T1

Review URL: https://codereview.chromium.org/1569353002

Cr-Commit-Position: refs/heads/master@{#33191}

src/mips/builtins-mips.cc

@@ -1423,8 +1423,8 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
     __ li(a1, Operand(Smi::FromInt(field_index)));
     __ CallCFunction(
         ExternalReference::get_date_field_function(masm->isolate()), 2);
-    __ Ret();
   }
+  __ Ret();
 
   // 3. Raise a TypeError if the receiver is not a date.
   __ bind(&receiver_not_date);

src/mips64/builtins-mips64.cc

@@ -1414,8 +1414,8 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
     __ li(a1, Operand(Smi::FromInt(field_index)));
     __ CallCFunction(
         ExternalReference::get_date_field_function(masm->isolate()), 2);
-    __ Ret();
   }
+  __ Ret();
 
   // 3. Raise a TypeError if the receiver is not a date.
   __ bind(&receiver_not_date);