ALSA: hda - Fix pin-detection in patch_sigmatel.c

The pin-detection function used in patch_sigmatel.c shouldn't be specific
to HP pin because it's used for input pins in general, too.

This patch fixes the detection function, removes the HP check from it
and moves to stac92xx_hp_detect().

Signed-off-by: Takashi Iwai <tiwai@suse.de>