mmc: fsl_esdhc_imx: set sysctl register for clock initialization

[ fsl_esdhc commit 263ddfc3 ]

The initial clock setting should be through sysctl register only,
while the mmc_set_clock() will call mmc_set_ios() introduce other
configurations like bus width, mode, and so on.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Sean Anderson <sean.anderson@seco.com>