drm/xe: Fix confusion with locals on context creation

drm/xe: Fix confusion with locals on context creation

After setting a local variable, check that local value rather that
checking destination at which the value will be stored later.

This fixes the obvious mistake in error path; without it,
allocation fail would lead to NULL dereference during context
creation.

Fixes: 89340099c6a4 ("drm/xe/lrc: Refactor context init into xe_lrc_ctx_init()")
Signed-off-by: Tomasz Lis <tomasz.lis@intel.com>
Cc: Raag Jadav <raag.jadav@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260320145733.1337682-1-tomasz.lis@intel.com