ALSA: Replace with fallthrough pseudo keyword in the remaining places

A few places (except for ASoC) are left unconverted for the new
fallthrough pseudo keyword.  Now replace them all.

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200709111750.8337-4-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>