[media] cx23885: remove use of deprecated current_norm

The use of current_norm can be dropped. The g_std ioctl was already
implemented, so current_norm didn't do anything useful anyway.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Steven Toth <stoth@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>