panfrost: Fix the damage box clamping logic

panfrost: Fix the damage box clamping logic

When the rendering are is not covering the whole FBO, and the biggest
damage rect is empty, we can have damage.max{x,y} > damage.min{x,y},
which leads to invalid reload boxes.

Fixes: 65ae86b85422 ("panfrost: Add support for KHR_partial_update()")
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3676>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3676>
(cherry picked from commit b550b7ef3b8d12f533b67b1a03159a127a3ff34a)