ALSA: hda/hdmi: Fix the converter reuse for the silent stream

When the user space pcm stream uses the silent stream converter,
it is no longer allocated for the silent stream. Clear the appropriate
flag in the hdmi_pcm_open() function. The silent stream setup may
be applied in hdmi_pcm_close() (and the error path - open fcn) again.

If the flag is not cleared, the reuse conditions for the silent
stream converter in hdmi_choose_cvt() may improperly share
this converter.

Cc: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220913070216.3233974-1-perex@perex.cz
Signed-off-by: Takashi Iwai <tiwai@suse.de>