[NFC] [X86] Fix scan-build complaining

Summary:
Remove unused variable. This fixes bug:
https://bugs.llvm.org/show_bug.cgi?id=42526



Signed-off-by: pengfei <pengfei.wang@intel.com>

Reviewers: RKSimon, xiangzhangllvm, craig.topper

Subscribers: cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D64389

llvm-svn: 365473