mpc85xx_edac: fix error: too few arguments to function 'edac_mc_alloc'

commit ca0907b9

 "edac: Remove the legacy EDAC ABI" broke mpc85xx_edac
in the following manner:

mpc85xx_edac.c:983:35: error: too few arguments to function 'edac_mc_alloc'

this patch puts back the missing 'layers' argument.

[mchehab@redhat.com: As Ben sent a similar fix, I added his SOB on this patch]
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Signed-off-by: Ben Collins <bcollins@ubuntu.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>