mmc: wbsd: Use new tasklet API

This converts the driver to use the new tasklet API introduced in
commit 12cc923f

 ("tasklet: Introduce new initialization API")

Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
Link: https://lore.kernel.org/r/20210204151847.91353-10-kernel@esmil.dk
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>