ALSA: hda - Fix a wrong busy check in alt PCM open

Currently, the alt PCM open callback returns -EBUSY when an
independent HP is turned off, supposing that it conflicts with the
main PCM.  However, obviously, this check is wrong when the
independent HP itself isn't enabled but the alt PCM was explicitly
created via alc_dac_nid by a codec driver.

Reported-and-tested-by: Kailang Yang <kailang@realtek.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>