[media] radio-bcm2048: use unlocked_ioctl instead of ioctl

This driver does its own locking, so there is no need to use
ioctl instead of unlocked_ioctl.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>