drm/xe: Fix NPD when saving default context

drm/xe: Fix NPD when saving default context

xef is only valid if it's a job from userspace.  For in-kernel jobs it
causes a NPD like below:

        <4> [] RIP: 0010:xe_sched_job_create+0xbd/0x390 [xe]
	...
        <4> [] Call Trace:
        <4> []  <TASK>
        <4> []  __xe_bb_create_job+0xa2/0x240 [xe]
        <4> []  ? find_held_lock+0x31/0x90
        <4> []  ? xa_find_after+0x12c/0x250
        <4> []  xe_bb_create_job+0x6e/0x380 [xe]
        <4> []  ? xa_find_after+0x136/0x250
        <4> []  ? __drm_dev_dbg+0x7d/0xb0
        <4> []  xe_gt_record_default_lrcs+0x542/0xb00 [xe]

Since drm_file starts with 1 for the unique id, just use 0 for the
in-kernel jobs.

Fixes: 2956554823ce ("drm/sched: Store the drm client_id in drm_sched_fence")
Cc: Christian König <christian.koenig@amd.com>
Cc: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Cc: Philipp Stanner <phasta@kernel.org>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://lore.kernel.org/r/20250528-fix-sched-v1-1-c042ef23ff8b@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>