sound, ca0106: Fix assignment to 'channel'.

The assignment to the local variable 'channel' in
snd_ca0106_pcm_pointer_capture() is a little crazy.  Order of assignment is
undefined. This fixes it.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>