[ALSA] Fix two typos and changes on snd_assert()

ALSA Core
Both typos were in the kerneldocs.

I splitted the snd_assert() calls in one-expression-per-call for better
debugging.

Signed-off-by: Henrik Kretzschmar <henne@nachtwindheim.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>