ARM64: Fix the atomic type width in the 64bit Acquire_Load().

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/220203012

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20486 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/atomicops_internals_arm64_gcc.h

@@ -309,7 +309,7 @@ inline Atomic64 NoBarrier_Load(volatile const Atomic64* ptr) {
 }
 
 inline Atomic64 Acquire_Load(volatile const Atomic64* ptr) {
-  Atomic32 value;
+  Atomic64 value;
 
   __asm__ __volatile__ (  // NOLINT
     "ldar %x[value], %[ptr]  \n\t"