drm/xe/tests: Set correct expectation

In xe_migrate_sanity_kunit test, use correct expected value as
the expected value was not only used for the xe_migrate_clear(),
but also for the xe_migrate_copy() operation.

v2: Add 'Fixes' tag and update commit text

Fixes: 11a2407e

 ("drm/xe: Stop accepting value in xe_migrate_clear")
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>