ALSA: aloop: Replace tasklet with work

The tasklet is an old API that should be deprecated, usually can be
converted to another decent API.  In aloop driver, a tasklet is still
used for offloading the timer event task.  It can be achieved
gracefully with a work queued, too.

This patch replaces the tasklet usage in aloop driver with a simple
work.

Link: https://lore.kernel.org/r/20200903104131.21097-6-tiwai@suse.de


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