[ALSA] pcm_oss: fix snd_pcm_oss_release() oops

Modules: ALSA<-OSS emulation

Fix Oops due to a typo in snd_pcm_oss.c.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>