drm/xe: Avoid touching consumer fields in GuC pagefault ack

drm/xe: Avoid touching consumer fields in GuC pagefault ack

The GuC pagefault acknowledgment code is designed to extract the fields
needed for the acknowledgment from the producer-stored message so that
the consumer fields can be overloaded to return additional information.
The ASID is stored in the producer message; extract it from there to
future‑proof this logic.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Francois Dugast <francois.dugast@intel.com>
Link: https://patch.msgid.link/20260212204227.2764054-3-matthew.brost@intel.com