sb_edac: Fix a typo and a thinko in address handling for Haswell

typo: "a7mode" chooses whether to use bits {8, 7, 9} or {8, 7, 6}
in the algorithm to spread access between memory resources. But
the non-a7mode path was incorrectly using GET_BITFIELD(addr, 7, 9)
and so picking bits {9, 8, 7}

thinko: BIT(1) of the dram_rule registers chooses whether to just
use the {8, 7, 6} (or {8, 7, 9}) bits mentioned above as they are,
or to XOR them with bits {18, 17, 16} but the code inverted the
test. We need the additional XOR when dram_rule{1} == 0.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Acked-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>