V4L/DVB (9936): cx18: Disable locking of Video and Audio PLL for analog captures

Disable AV_LOCK, locking of audio PLL to video PLL in the cx18-av-core for
analog captures.  It seems to have adverse effects on captures from
SVideo and CVBS sources with current clock & crystal settings in the driver.

Many thanks to Jeff Campbell and Mike Bradley for reporting this problem,
and suggesting the solution and performing extensive testing to support their
suggestion.

Reported-by: Jeff Campbell <jac1dlists@gmail.com>
Reported-by: Mike Bradley <mike.bradley@incanetworks.com>
Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>