ASoC: sh: Replace tasklet with work

The tasklet is an old API that should be deprecated, usually can be
converted to another decent API.  In ASoC SH SIU driver, a tasklet is
still used for offloading the hardware reset function.  It can be
achieved gracefully with a work queued, too.

This patch replaces the tasklet usage in SH SIU driver with a simple
work.  The conversion is fairly straightforward.

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