ALSA: pcm - Fix unbalanced pm_qos_request

The pm_qos_request isn't freed properly when OSS PCM emulation is used
because it skips snd_pcm_hw_free() call but directly releases the
stream.  This resulted in Oops later.

Tested-by: Simon Kirby <sim@hostway.ca>
Signed-off-by: Takashi Iwai <tiwai@suse.de>