With the previous patch drm_crtc_find will return NULL when the crtc
isn't in our lease, which will then disable the plane/connector. No
longer an issue since the lessor can't escape their lease terms
anymore, but not quite great semantics yet either.

Catch this and return -EACCES, so that at least evil test cases have a
better chance of making sure the kernel works correctly.
Reviewed-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190228144910.26488-8-daniel.vetter@ffwll.ch