Staging: cx25821: Rename member name in struct cx25821_dev

Rename _audio_upstream_channel_select to _audio_upstream_channel in
in struct cx25821_dev in cx25821.h and all usages of that struct member
as well, because _audio_upstream_channel_select is seems to be too long
for a variable name.

Signed-off-by: Leonid V. Fedorenchik <leonidsbox@gmail.com>
Reviewed-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Reviewed-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>