[media] BKL: trivial BKL removal from V4L2 radio drivers

The patch converts a bunch of V4L2 radio drivers to unlocked_ioctl.

These are all simple conversions: most already had a lock and so the ioctl
fop could simply be replaced by unlocked_ioctl.

radio-miropcm20.c was converted to use the new V4L2 core lock.

While doing this work I noticed that many of these drivers initialized
some more fields or muted audio or something like that *after* creating
the device node. This should be done before the device node is created
to prevent problems. Especially hal tends to grab a device node as soon
as it is created.

In one or two cases the mutex_init was even done after the device creation!

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>