UPSTREAM: ALSA: timer: Call notifier in the same spinlock

UPSTREAM: ALSA: timer: Call notifier in the same spinlock

snd_timer_notify1() is called outside the spinlock and it retakes the
lock after the unlock.  This is rather racy, and it's safer to move
snd_timer_notify() call inside the main spinlock.

The patch also contains a slight refactoring / cleanup of the code.
Now all start/stop/continue/pause look more symmetric and a bit better
readable.

Bug: 37240993
Change-Id: Ib90099f88c8b04928a8cdd2808cd9e16da6d519c
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Siqi Lin <siqilin@google.com>