EDAC/sb_edac: Fix top-of-high-memory value for Broadwell/Haswell

The computation of TOHM is off by one bit. This missed bit results in
too low a value for TOHM, which can cause errors in regular memory to
incorrectly report:

  EDAC MC0: 1 CE Error at MMIOH area, on addr 0x000000207fffa680 on any memory

Fixes: 50d1bb93 ("sb_edac: add support for Haswell based systems")
Cc: stable@vger.kernel.org
Reported-by: Meeta Saggi <msaggi@purestorage.com>
Signed-off-by: Eric Badger <ebadger@purestorage.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20211010170127.848113-1-ebadger@purestorage.com