ALSA: allocation may fail in snd_pcm_oss_change_params()

Allocation may fail, show if it did.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
[Additional fix for invalid runtime->oss.prepare flag set by tiwai]
Signed-off-by: Takashi Iwai <tiwai@suse.de>