sb_edac: Fix erroneous bytes->gigabytes conversion

commit 8c009100295597f23978c224aec5751a365bc965 upstream.

Signed-off-by: Jim Snow <jim.snow@intel.com>
Signed-off-by: Lukasz Anaczkowski <lukasz.anaczkowski@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Vinson Lee <vlee@twopensource.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>