gbm/dri: Fix leaking bo memory on failure path

gbm/dri: Fix leaking bo memory on failure path

In gbm_dri_bo_create, when modifiers are requested but not supported, do
not return NULL immediately, but first go to cleanup section to free
already allocated buffer object.

Fixes: cb9ae4273d68 ("dri: add loader_dri_create_image helper")
Signed-off-by: Heinrich Fink <hfink@snap.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Simon Ser <contact@emersion.fr>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11844>