In the error path, ata_device_add()

* dereferences null host_set->ports[] element.
* calls scsi_remove_host() on not-yet-added shost.

This patch fixes both bugs.  The first problem was spotted and initial
patch submitted by Dave Jones <davej@redhat.com>.  The second problem
was mentioned and fixed by Jeff Garzik <jgarzik@pobox.com> in a larger
cleanup patch.

Cc: Dave Jones <davej@redhat.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>