V4L/DVB (9457): Optimization, Fix a Bug

* cut down some I/O operations by disabling "disable gate"
* budget_av was left with the gate open, thereby more susceptible
to RF interference due to I/O operations

Signed-off-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>