MdeModulePkg: Fix build warning on Xhci driver with XCode 32 tool chain.

Signed-off-by: Tian Feng <feng.tian@intel.com>
Reviewed-by: Sun Rui <rui.sun@intel.com>

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13177 6f19259b-4bc3-4df7-8a09-765794883524
1 file changed