ALSA: emux: remove unused redundant variable p2

The variable p2 is being assigned but never used, it is redundant
and can be safely removed.  Cleans up clang warning: Value stored to
'p2' is never read.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>