Simplify StringCharCodeAt in non-crankshaft codegen.

src/arm/ic-arm.cc

Index: src/arm/ic-arm.cc
diff --git a/src/arm/ic-arm.cc b/src/arm/ic-arm.cc
index 18d4a9fa8b5cfefc083b7243dd9013c439d2c0fe..f8e4bbb6bafcb0e4c279ef2c31efbd0c51de574d 100644
--- a/src/arm/ic-arm.cc
+++ b/src/arm/ic-arm.cc
@@ -1109,14 +1109,12 @@ void KeyedLoadIC::GenerateString(MacroAssembler* masm) {
 
   Register receiver = r1;
   Register index = r0;
-  Register scratch1 = r2;
-  Register scratch2 = r3;
+  Register scratch = r3;
   Register result = r0;
 
   StringCharAtGenerator char_at_generator(receiver,
                                           index,
-                                          scratch1,
-                                          scratch2,
+                                          scratch,
                                           result,
                                           &miss,  // When not a string.
                                           &miss,  // When not a number.