When pata_legacy can't detect any device, it unregisters the
platform_device and fails detection. However, it forgets to detach
ata host triggering weird failures as the host later gets freed by
devres while still attached. Fix it.
Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Jeff Garzik <jgarzik@redhat.com>