ALSA: hda: Initialize power_state field properly

The recent commit 98081ca6 ("ALSA: hda - Record the current power
state before suspend/resume calls") made the HD-audio driver to store
the PM state in power_state field.  This forgot, however, the
initialization at power up.  Although the codec drivers usually don't
need to refer to this field in the normal operation, let's initialize
it properly for consistency.

Fixes: 98081ca6 ("ALSA: hda - Record the current power state before suspend/resume calls")
Signed-off-by: Takashi Iwai <tiwai@suse.de>