V4L/DVB (13402): radio-mr800 - autosuspend for radio-mr800 driver

Patch adds autosuspend support for mr800 radio driver.

Signed-off-by: Oliver Neukum <oliver@neukum.org>
Acked-by: Alexey Klimov <klimov.linux@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>