ALSA: timer: Make snd_timer_close() returning void

The function doesn't return any useful value, so let's make it void to
be clearer.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20191107192008.32331-3-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>