[ALSA] emu10k1 - Check value ranges in ctl callbacks

Check value ranges in ctl callbacks properly.  This fixes the unexpected
crash due to wrong value assignment.
Also, remove invalid comments in the last patch.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>