ALSA: pcm: Avoid double hw_free calls at releasing a stream

snd_pcm_release_substream() always calls hw_free op when the stream
was opened.  This is superfluous in most cases because it's been
already released via explicit hw_free ioctl.  Although this double
call is usually OK as this callback should be written to be called
multiple times, it's better to avoid superfluous calls.

Reported-by: Vinod Koul <vinod.koul@intel.com>
Tested-by: Jeeja Kp <jeeja.kp@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>