ALSA: core: Remove superfluous exit calls for proc entries

Since each proc entry is freed automatically by the parent, we don't
have to take care of its life cycle any longer.  This allows us to
reduce a few more lines of codes.

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