OMAP3 clock/SDRC: program SDRC_MR register during SDRC clock change

Program the SDRC_MR_0 register as well during SDRC clock changes.
This register allows selection of the memory CAS latency.  Some SDRAM
chips, such as the Qimonda HYB18M512160AF6, have a lower CAS latency
at lower clock rates.

Signed-off-by: Paul Walmsley <paul@pwsan.com>