ALSA: hda - Fix error check from snd_hda_get_conn_index() in patch_cirrus.c

snd_hda_get_conn_index() returns a negative value while the current code
stores it in an unsigned int.  It must be stored in a signed integer.

Reported-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>