drm/udl: properly check for error pointers
drm/udl: properly check for error pointers

The drm_prime_pages_to_sg() function never returns NULL pointers, only
error pointers and valid pointers.

Signed-off-by: Haixia Shi <40e52e374a4d2db23e8a992704b364aaabfeb552@chromium.org>
Reviewed-by: Stéphane Marchesin <e16f69845633a0cf74affe1e5a677caa6296c937@chromium.org>
Signed-off-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs