EDAC, amd64: Fix reporting of Chip Select sizes on Fam17h

The wrong index into the csbases/csmasks arrays was being passed to
the function to compute the chip select sizes, which resulted in the
wrong size being computed. Address that so that the correct values are
computed and printed.

Also, redo how we calculate the number of pages in a CS row.

Reported-by: Benjamin Bennett <benbennett@gmail.com>
Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Cc: <stable@vger.kernel.org> # 4.10.x
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1493313114-11260-1-git-send-email-Yazen.Ghannam@amd.com
[ Remove unneeded integer math comment, minor cleanups. ]
Signed-off-by: Borislav Petkov <bp@suse.de>