edac: ppc mpc85xx fix mc err detect

Error found by Jeff Haran.

The error detect register is 0s when no errors are detected.  The check
code is incorrect, so reverse check sense.

Reported-by: Jeff Haran <jharan@Brocade.COM>
Signed-off-by: Dave Jiang <djiang@mvista.com>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>