mmc: dw_mmc: update actual clock for mmc debugfs

mmc: dw_mmc: update actual clock for mmc debugfs

Respect the actual clock for mmc debugfs to help better debug
the hardware.

mmc_host mmc0: Bus speed (slot 0) = 135475200Hz (slot req 150000000Hz,
actual 135475200HZ div = 0)

cat /sys/kernel/debug/mmc0/ios
clock:          150000000 Hz
actual clock:   135475200 Hz
vdd:            21 (3.3 ~ 3.4 V)
bus mode:       2 (push-pull)
chip select:    0 (don't care)
power mode:     2 (on)
bus width:      3 (8 bits)
timing spec:    9 (mmc HS200)
signal voltage: 0 (1.80 V)
driver type:    0 (driver type B)

Cc: Xiao Yao <xiaoyao@rock-chips.com>
Cc: Ziyuan <xzy.xu@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>