There are two bugs in disabled port handling.

* test in PORT_PATA0 is reversed
* ->prereset should return -ENOENT for disabled ports not 0

The first bug makes the PATA channel considered disabled but the
second bug saves the day by returning 0.  The net result is that cable
is always left at ATA_CBL_UNKNOWN.  This results in false 80c
configuration and thus transfer errors.

This patch fixes both bugs.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>