drm/xe: Remove unrequired NULL check in xe_sched_job_free_fences

drm/xe: Remove unrequired NULL check in xe_sched_job_free_fences

dma_fence_chain_free() can handle NULL input, there is no need for NULL
check by caller.

Signed-off-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Jagmeet Randhawa <jagmeet.randhawa@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240820090230.3258128-3-himal.prasad.ghimiray@intel.com
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>