sb_edac: remove bogus assumption on mc ordering

When a MC is handled, the correct sbridge_dev is searched based on the node,
checking again later with the assumption the first memory controller found is
the first socket's memory controller is a bogus assumption. Get rid of it.

Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>