ALSA: pcm: Fix mutex unbalance in OSS emulation ioctls

The previous fix 40cab6e8 ("ALSA: pcm: Return -EBUSY for OSS
ioctls changing busy streams") introduced some mutex unbalance; the
check of runtime->oss.rw_ref was inserted in a wrong place after the
mutex lock.

This patch fixes the inconsistency by rewriting with the helper
functions to lock/unlock parameters with the stream check.

Fixes: 40cab6e8

 ("ALSA: pcm: Return -EBUSY for OSS ioctls changing busy streams")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>