Revert "pata_atiixp: Don't use unconnected secondary port on SB600/SB700"

This reverts commit 5946fdae.

The original commit's assumption that the secondary port is
unconnected turns out to be false.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Markku Pesonen <tourula@gmail.com>
Fixes: 5946fdae ("pata_atiixp: Don't use unconnected secondary port on SB600/SB700")
Cc: Darren Stevens <darren@stevens-zone.net>