sb_edac: Fix erroneous bytes->gigabytes conversion

[ Upstream commit ece9210859abb2cc0126f8adbfbbdee668d4906a ]

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>
[ vlee: Backported to 3.14. Adjusted context. ]
Signed-off-by: Vinson Lee <vlee@twitter.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>