mmc: fsl_esdhc_imx: check the clock stable status after config the clock rate.

Currently, after config the clock rate, delay 10ms, this is quite a rough
method. Check the clock stable status in the present status register is
enough.

Tested-by: Ji Luo <ji.luo@nxp.com>
Signed-off-by: Haibo Chen <haibo.chen@nxp.com>