When changing channels the audio has to be muted. This is done 
by calling CX2341X_ENC_MUTE_AUDIO and by muted the audio input. 
The latter is not necessary and is now removed.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>