bttv: fix s_tuner for radio

commit a024c1a6 upstream.

Fix typo: g_tuner should have been s_tuner.

Tested with a bttv card.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>