drm/panfrost: Don't try to map on error faults

If the exception type isn't a translation fault, don't try to map and
instead go straight to a terminal fault.

Otherwise, we can get flooded by kernel warnings and further faults.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>