libata-pmp-prep: implement EH fast-fail path

If PMP itself becomes inaccessible while trying to link a downstream
link, spending time to recover the downstream link doesn't make any
sense.  Make EH skip retry and fail fast if -ERESTART is received.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>