mmc: sdhci-esdhc-imx: set actual_clock in clock setting

This enables access the actual_clock via sys.
root@imx6qsabreauto:~# cat /sys/kernel/debug/mmc0/ios
clock:          198000000 Hz
actual clock:   198000000 Hz
vdd:            17 (2.9 ~ 3.0 V)
bus mode:       2 (push-pull)
chip select:    0 (don't care)
power mode:     2 (on)
bus width:      2 (4 bits)
timing spec:    6 (sd uhs SDR104)
signal voltage: 0 (1.80 V)

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>