mmc: renesas_sdhi_internal_dmac: clean up the code for dma complete

To add end() operation in the future, clean the code of
renesas_sdhi_internal_dmac_complete_tasklet_fn(). No behavior change.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Link: https://lore.kernel.org/r/1590044466-28372-3-git-send-email-yoshihiro.shimoda.uh@renesas.com
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>