MIPS: Fix Add a MathFloor stub generated with TurboFan.

src/mips/interface-descriptors-mips.cc

Index: src/mips/interface-descriptors-mips.cc
diff --git a/src/mips/interface-descriptors-mips.cc b/src/mips/interface-descriptors-mips.cc
index 09413e70871b95bf0fb79d6b36243ef185e440bc..e02b9759c5114dd0621fa3851e7e7561145d04dd 100644
--- a/src/mips/interface-descriptors-mips.cc
+++ b/src/mips/interface-descriptors-mips.cc
@@ -373,8 +373,8 @@ void ApiAccessorDescriptor::Initialize(CallInterfaceDescriptorData* data) {
 
 void MathRoundVariantDescriptor::Initialize(CallInterfaceDescriptorData* data) {
   Register registers[] = {
-      a1,  // context
-      a2,  // math rounding function
+      cp,  // context
+      a1,  // math rounding function
       a3,  // vector slot id
   };
   Representation representations[] = {