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.

Fixes: 187d2929

 ("drm/panfrost: Add support for GPU heap allocations")
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Acked-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212202236.13095-1-robh@kernel.org