alsa: fix snd_BUG_on() and friends

sound/pci/pcxhr/pcxhr_core.c: In function 'pcxhr_set_pipe_cmd_params':
sound/pci/pcxhr/pcxhr_core.c:700: warning: statement with no effect
sound/pci/pcxhr/pcxhr_core.c:706: warning: statement with no effect
sound/pci/pcxhr/pcxhr_core.c:710: warning: statement with no effect

Due to

try to fix this, and be more conventional about the empty stubs.

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>