[media] lirc_dev: make fops mandatory

Every caller of lirc_register_driver() passes their own fops and there
are no users of lirc_dev_fop_write() in the kernel tree. Thus we can
make fops mandatory and remove lirc_dev_fop_write().

Signed-off-by: David Härdeman <david@hardeman.nu>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>