mmc: dw_mmc: Make sure we only adjust the clock when power is on

It appears that we can confuse things if we try to turn on the MMC
clock when the power is off.  Adjust is so that we turn the clock on
(using dw_mci_setup_bus) after power is all the way on and we turn the
clock off before the power goes off.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>