V4L/DVB (6338): ivtv: fix incorrect EBUSY return

Trying to open the radio when a capture is in progress will make it
impossible to open the radio again since the radio stream wasn't released.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>