V4L/DVB (7761): ivtv: increase the DMA timeout from 100 to 300 ms

When there is a lot of DMA traffic this timeout might sometimes be too low.
Increase it to be on the safe side.

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