mmc: esdhc: Workaround for data crc error on p1010rdb

SD card read was failing (data crc error) on some cards at
maximum possible frequency on P1010 (CCB frequency set to 400MHz).
Some clock deviations are also observed at this frequency.
Hence reduced the mmc clock freq.

Signed-off-by: Priyanka Jain <Priyanka.Jain@freescale.com>
Singed-off-by: Jerry Huang <Chang-Ming.Huang@freescale.com>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>