[media] radio-bcm2048: Fix region selection

This patch fixes region selection for lower bottom_frequency in BCM2048 FM
receiver. It also removes "Japan wide band" region since this is impossible
to do just like that.

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