ALSA: hdsp: Replace tasklet with work

ALSA: hdsp: Replace tasklet with work

The tasklet is an old API that should be deprecated, usually can be
converted to another decent API.  In HDSP driver, a tasklet is still
used for offloading the MIDI I/O handling (optional via mixer
switch).  It can be achieved gracefully with a work queued, too.

This patch replaces the tasklet usage in HDSP driver with a simple
work.  The conversion is fairly straightforward.  The only significant
difference is that a superfluous tasklet_kill() call is removed from
snd_hdap_midi_input_trigger().

Link: https://lore.kernel.org/r/20200903104131.21097-7-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>