drivers/edac/mpc85xx_edac.c: fix memory controller compatible for edac

compatible in dts has been changed, so the driver needs to be updated
accordingly.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>