ata_host_detach() detaches an attached port and shouldn't be called on
a port which hasn't been attached yet.  pata_legacy incorrectly calls
ata_host_detach() on unattached port after initialization failure
causing oops.  Fix it.
Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>