Fix has_constant_parameter_count() confusion in LReturn

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index c9e3686c9e1bf5e76a208522aaf0a5faeb3a37be..07f32de344b4f2049b2adef7a9b3b7068eeb68d4 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -2858,6 +2858,7 @@ void LCodeGen::DoReturn(LReturn* instr) {
       __ Addu(sp, sp, Operand(sp_delta));
     }
   } else {
+    DCHECK(info()->IsStub());  // Functions would need to drop one more value.
     Register reg = ToRegister(instr->parameter_count());
     // The argument count parameter is a smi
     __ SmiUntag(reg);