[ALSA] Handle the error correctly in SNDCTL_DSP_SETFMT ioctl

Handle the error returned from snd_pcm_oss_get_formats() correctly
in SNDCTL_DSP_SETFMT ioctl handler of PCM OSS emulation.

Signed-off-by: Steven Finney <sfinney@healthhero.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>