video: fbdev: matrox: the list iterator can't be NULL

My static checker is complaining because we check "drv" for NULL and
then we dereference it to get the next item in the list.  It can't be
NULL so we can remove this check.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>