[media] firedtv-avc: Fix compilation warnings

drivers/media/dvb/firewire/firedtv-avc.c: In function ‘avc_tuner_tuneqpsk’:
drivers/media/dvb/firewire/firedtv-avc.c:394:4: warning: enumeration value ‘ROLLOFF_15’ not handled in switch [-Wswitch]
drivers/media/dvb/firewire/firedtv-avc.c:394:4: warning: enumeration value ‘ROLLOFF_13’ not handled in switch [-Wswitch]

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>