libata: use __ratelimit

Use __ratelimit() instead of its own private rate limit implementation.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Jeff Garzik <jgarzik@pobox.com>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>