[ALSA] Don't set up the same PID twice in snd_hda_multi_out_analog_prepare

Check the hp_nid whether it's identical with front pin to avoid
the setup of the same widget node twice.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>