mmc: dw_mmc: shift with slot-id for CLKENA register

In CLKENA register, can support 16-SD card clocks.
If support correctly, must shift with slot-id.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Will Newton <will.newton@imgtec.com>
Signed-off-by: Chris Ball <cjb@laptop.org>