ALSA: hdsp - Fix potential Oops in snd_hdsp_info_pref_sync_ref()

Dan Carpenter reported that setting 0 to uinfo->value.enumerated.items
in snd_hdsp_info_pref_sync_ref() may lead to Oops.  This function should
return an error immediately in such a case instead.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>