[media] cobalt: fix irqs used for the adv7511 transmitter

The interrupt bit assignments use for the adv7511 were off by one.
This means that the current scheme (bit << (4 * stream_index)) can
no longer be used.

Fix this by precalculating and storing the correct masks in the
cobalt_stream struct.

This wasn't noticed before because the adv7511 interrupts are very
rare. But for CEC support these interrupts are essential, so this made
me realize that it wasn't working correctly.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>