libata: wrap schedule_timeout_uninterruptible() in loop

Tasks in uninterruptible sleep might be woken up by unrelated events
and should check whether the condition it was waiting for has actually
triggered.  Wrap schedule_timeout_uninterruptible() in loop to achieve
it.

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