MdeModulePkg/UsbBusDxe: Fixed Clang build error.

Contributed-under: TianoCore Contribution Agreement 1.0

Signed-off-by: Nikolai Saoukh <nms@otdel-1.org>
Reviewed-by: Feng Tian <feng.tian@intel.com>

git-svn-id: svn://svn.code.sf.net/p/edk2/code/trunk/edk2/MdeModulePkg@16084 6f19259b-4bc3-4df7-8a09-765794883524