For a legacy ATA controller, libata registers two separate host sets.
There was no connection between the two hosts making it impossible to
traverse all ports related to the controller.  This patch adds
host_set->next which points to the second host_set and makes
ata_pci_remove_one() remove all associated host_sets.

* On device removal, all ports hanging off the device are properly
  detached.  Prior to this patch, ports on the first host_set weren't
  detached casuing oops on driver unloading.

* On device removal, both host_sets are properly freed

This will also be used by new power management code to suspend and
resume all ports of a controller.  host_set/port representation will
be improved to handle legacy controllers better and this host_set
linking will go away with it.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>