V4L/DVB (10743): dm1105: not demuxing from interrupt context.

The driver already has DMA buffer organized like ringbuffer,
so it is easy to switch to a work queue.
Length of ringbuffer can easily be increased, if someone need it.

Signed-off-by: Igor M. Liplianin <liplianin@netup.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>