[media] au8522: improve lock performance with ZeeVee modulators

Improves lock performance with signals from the ZeeVee family
of modulators.

Signed-off-by: Richard Vollkommer <linux@hauppauge.com>
Cc: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Michael Ira Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>