[media] saa7134: use unlocked_ioctl instead of ioctl

The saa7134 driver uses core-locking, so there is no longer any need
to use the ioctl op instead of the unlocked_ioctl op. This change
was forgotten for the saa7134-empress.c, so fix this.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>