Fix poisoining bug in arm64.

Change-Id: I30ca7f237009d81c9d83fabb6a4c76bf4c74d451
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 60315ec..c081e11 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -1719,7 +1719,7 @@
       if (!index.IsConstant()) {
         __ Add(temp, array, offset);
       }
-      __ Str(value, destination);
+      __ Str(source, destination);
 
       if (!may_need_runtime_call) {
         codegen_->MaybeRecordImplicitNullCheck(instruction);