arm: socfpga: mmc: Pick the clock from clock manager

arm: socfpga: mmc: Pick the clock from clock manager

Make the SoCFPGA MMC stub pick clock via the clock manager
frequency accessors instead of hard-coding the frequency.

Also fix calloc() misuse.

Signed-off-by: Pavel Machek <[email protected]>
Signed-off-by: Marek Vasut <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Albert Aribaud <[email protected]>
Cc: Tom Rini <[email protected]>
Cc: Wolfgang Denk <[email protected]>
Cc: Pavel Machek <[email protected]>
Acked-by: Dinh Nguyen <[email protected]>