V4L/DVB (10054): dsbr100: fix unplug oops

This patch corrects unplug procedure. Patch adds
usb_dsbr100_video_device_release, new macros - videodev_to_radio, mutex
lock and a lot of safety checks.
Struct video_device videodev is embedded in dsbr100_device structure.

Signed-off-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>