Opt compiler: ARM64: Fix blocking fp registers.

VIXL reserved float point registers has not been blocked correctly.

Change-Id: Ie7131d86bbaff48c431e3e26abd2fa26389ac687
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 46f1a9b..ec716a4 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -577,7 +577,7 @@
   }
 
   CPURegList reserved_fp_registers = vixl_reserved_fp_registers;
-  while (!reserved_core_registers.IsEmpty()) {
+  while (!reserved_fp_registers.IsEmpty()) {
     blocked_fpu_registers_[reserved_fp_registers.PopLowestIndex().code()] = true;
   }