V4L/DVB (6050): ivtv: retry/timer improvements

- Give up frame after three retries.
- When the last capture/decode ends, make sure to delete the dma_timer.

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