OSS: soundcard: locking bug in sound_ioctl()

We shouldn't return directly here because we're still holding the
&soundcard_mutex.

This bug goes all the way back to the start of git.  It's strange that
no one has complained about it as a runtime bug.

CC: stable@kernel.org
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>