V4L/DVB: drivers/media/dvb/dvb-usb/dib0700: fix return values

Propagte correct error values instead of returning -1 which just means
-EPERM ("Permission denied")

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>