drm/xe/vf: Fix IS_ERR() vs NULL check in xe_sriov_vf_ccs_init()

The xe_migrate_alloc() function returns NULL on error.  It doesn't return
error pointers.  Update the checking to match.

Fixes: a843b989 ("drm/xe/vf: Fix VM crash during VF driver release")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/r/aIzB8-Y6wtZvfNQT@stanley.mountain


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>