pdc_adma: kill adma_host_stop()

adma_host_stop() does the same thing that adma_port_stop() does.  Kill
it.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Mark Lord <liml@rtr.ca>
Signed-off-by: Jeff Garzik <jeff@garzik.org>