drm/xe: Fix uninitialized return values

clang warned about two uninitialized variables used as return
values in the exhaustive eviction series.

Fix those.

Fixes: 1f154172 ("drm/xe: Rework instances of variants of xe_bo_create_locked()")
Fixes: 7bcb6e38 ("drm/xe/display: Convert __xe_pin_fb_vma()")
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Link: https://lore.kernel.org/r/20250910151128.49693-1-thomas.hellstrom@linux.intel.com