ARMV7: S5P: Fixed register offset in mmc.h

The MMC registers are accessed through struct s5p_mmc member
variables. MMC controller "control4" register offset is set
to 0x8C as per data sheet. The size of struct s5p_mmc is also
corrected.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Signed-off-by: Tushar Behera <tushar.behera@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>