Move Method shorty to managed heap

Change-Id: Iafd05502b498c823063d0603915a92db8c95f060
diff --git a/src/jni_internal_arm.cc b/src/jni_internal_arm.cc
index ed42c12..65dc380 100644
--- a/src/jni_internal_arm.cc
+++ b/src/jni_internal_arm.cc
@@ -101,7 +101,7 @@
   __ blx(IP);
 
   // If the method returns a value, store it to the result pointer.
-  char ch = method->GetShorty()[0];
+  char ch = method->GetShorty()->CharAt(0);
   if (ch != 'V') {
     // Load the result JValue pointer of the stub caller's out args.
     __ LoadFromOffset(kLoadWord, IP, SP, frame_size);