MAINTAINERS: update EDAC entry to reflect current tree and maintainers

Tony will start to officially maintain EDAC trees. Also, we'll
be using a single tree for the EDAC development.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Tony Luck <tony.luck@intel.com>