edac: add MAINTAINERS entry for i5400 EDAC driver

i5400 EDAC driver were added upstream by those changesets:

 - 920c8df6 "edac: driver for i5400 MCH (Seaburg)"
 - 8375d490

 "edac: driver for i5400 MCH (update)"

Update MAINTAINERS entry for this file to correspond to the driver
maintainer.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Cc: Ben Woodard <woodard@redhat.com>
Cc: Doug Thompson <norsk5@yahoo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>