mmc: fsl_esdhc: fix f_max retrieval during init

for multi instance API we use struct fsl_esdhc_cfg to
pass the clock rate. Do not set f_max from global data,
since this is wrong for multi instance case.

Signed-off-by: Markus Niebel <Markus.Niebel@tq-group.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Tested-by: Eric Nelson <eric.nelson@boundarydevices.com>
Reviewed-by: York Sun <yorksun@freescale.com>