drm/vkms: plane_state->fb iff plane_state->crtc

Checking both is one too much, so wrap a WARN_ON around it to stope
the copypasta.
Reviewed-by: Rodrigo Siqueira <rodrigosiqueira@gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueira@gmail.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191213172612.1514842-9-daniel.vetter@ffwll.ch

drivers/gpu/drm/vkms/vkms_plane.c

@@ -117,7 +117,7 @@ static int vkms_plane_atomic_check(struct drm_plane *plane,
 	bool can_position = false;
 	int ret;
 
-	if (!state->fb | !state->crtc)
+	if (!state->fb || WARN_ON(!state->crtc))
 		return 0;
 
 	crtc_state = drm_atomic_get_crtc_state(state->state, state->crtc);