mmc: dw_mmc: rockchip: remove incorrect __exit_p()

dw_mci_pltfm_remove() is not (nor should it be) marked as __exit,
so we should not be using __exit_p() wrapper with it.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Tested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>