mmc: fsl_esdhc: set sysctl register for clock initialization

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>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>