mmc: fsl_esdhc_imx: fix mmc->clock with actual clock

[ fsl_esdhc commit 30f6444d ]

Fix mmc->clock with actual clock which is divided by the
controller, and record it with priv->clock.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>