ata_dev_knobble() unconditionally used the first device of the port to
determine whether a device is bridged or not.  This causes bridge
limit to be incorrectly applied or unapplied for hosts with slave
devices (e.g. ata_piix).
Signed-off-by: NTejun Heo <htejun@gmail.com>
Signed-off-by: NJeff Garzik <jgarzik@pobox.com>