mmc: dw_mmc: remove redundant of set_bit and clear_bit

dw_mci_get_cd have already dealt with these for
both of internal card-detect and gpio card-detect.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>