panfrost: Simplify panfrost_resource_get_handle

panfrost: Simplify panfrost_resource_get_handle

Unify the exit paths to clean up the logic. There are logically three modes we
support (KMS without renderonly, KMS with renderonly, and FD); these each
correspond to a leg of a small if statement. Outside of the small if's,
everything else should be identical.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Reviewed-by: James Jones <jajones@nvidia.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15120>