V4L/DVB (11954): dsbr100: remove radio->users counter

Patch removes radio->users counter because it is not in use.

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>