Clean up String.indexOf() intrinsics.

Additional cleanup after
    https://android-review.googlesource.com/223260

Bug: 28330359
Change-Id: I88def196babec70123896ef581ec8d61bb1b9a9a
diff --git a/compiler/optimizing/intrinsics_mips64.cc b/compiler/optimizing/intrinsics_mips64.cc
index 7188e1c..6c4e64e 100644
--- a/compiler/optimizing/intrinsics_mips64.cc
+++ b/compiler/optimizing/intrinsics_mips64.cc
@@ -1568,7 +1568,7 @@
   SlowPathCodeMIPS64* slow_path = nullptr;
   HInstruction* code_point = invoke->InputAt(1);
   if (code_point->IsIntConstant()) {
-    if (!IsUint<16>(invoke->InputAt(1)->AsIntConstant()->GetValue())) {
+    if (!IsUint<16>(code_point->AsIntConstant()->GetValue())) {
       // Always needs the slow-path. We could directly dispatch to it,
       // but this case should be rare, so for simplicity just put the
       // full slow-path down and branch unconditionally.