EDAC, mv64x60: Check driver registration success

Check the return status of platform_driver_register() in
mv64x60_edac_init(). Only output messages and initialise the
edac_op_state if the registration is successful.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/20170529212142.25572-2-chris.packham@alliedtelesis.co.nz


Signed-off-by: Borislav Petkov <bp@suse.de>