drm/xe/ufence: Prefetch ufence addr to catch bogus address

In the Linux kernel, the following vulnerability has been resolved: drm/xe/ufence: Prefetch ufence addr to catch bogus address access_ok() only checks for addr overflow so also try to read the addr to catch invalid addr sent from userspace. (cherry picked from commit 9408c4508483ffc60811e910a93d6425b8e63928)