drm/xe: Use helper for ASID -> VM in GPU faults and access counters

Normalize both code paths with a helper. Fixes a possible leak access
counter path too.

Suggested-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240918160503.2021315-1-matthew.brost@intel.com