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.czSigned-off-by: Takashi Iwai <tiwai@suse.de>