[AArch64] Fix a type conversion bug for anlyzing compare.

The bug can cause spec2006/483.xalancbmk failure.

Patched by David Xu.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215206 91177308-0d34-0410-b5e6-96231b3b80d8