ALSA: hda - Check power-state before changing in patch_via.c

Instead of always writing AC_VERB_SET_POWER_STATE, check the current
power-state and don't write again if the value is already set.
This may reduce the click noise upon the dynamic power-state change
(e.g. in analog-input mixer).
Signed-off-by: Takashi Iwai <tiwai@suse.de>