V4L/DVB (6832): cx88-blackbird: don't mute audio when stopping the codec

We should not mute the audio input when we stop the codec,
because it will interfere with the live uncompressed stream.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Reviewed-by: Jelle Foks <jelle@foks.8m.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>