V4L/DVB (9306): dsbr100: Add frequency check

Add checking for frequency and printk if -1 returned.

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