ALSA: hda - Cache the MUX selection for generic HDMI

When a selection to a converter MUX is changed in hdmi_pcm_open(), it
should be cached so that the given connection can be restored properly
at PM resume.  We need just to replace the corresponding
snd_hda_codec_write() call with snd_hda_codec_write_cache().

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>