drm/atomic: Clear crtcs, connectors and planes when clearing state

Users of the atomic state assume that if the pointer to a crtc, plane or
connector is not NULL in the respective object vector, than the state
for that object in *_states vector also won't be NULL. That assumption
was broken by drm_atomic_state_clear(), which would clear the state
pointer but leave the pointer to the object still set.

This fixes a NULL pointer dereference in i915 caused by the use of
drm_atomic_state_clear().

Cc: dri-devel@lists.freedesktop.org
Signed-off-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic.c

@@ -134,6 +134,7 @@ void drm_atomic_state_clear(struct drm_atomic_state *state)
 
 		connector->funcs->atomic_destroy_state(connector,
 						       state->connector_states[i]);
+		state->connectors[i] = NULL;
 		state->connector_states[i] = NULL;
 	}
 
@@ -145,6 +146,7 @@ void drm_atomic_state_clear(struct drm_atomic_state *state)
 
 		crtc->funcs->atomic_destroy_state(crtc,
 						  state->crtc_states[i]);
+		state->crtcs[i] = NULL;
 		state->crtc_states[i] = NULL;
 	}
 
@@ -156,6 +158,7 @@ void drm_atomic_state_clear(struct drm_atomic_state *state)
 
 		plane->funcs->atomic_destroy_state(plane,
 						   state->plane_states[i]);
+		state->planes[i] = NULL;
 		state->plane_states[i] = NULL;
 	}
 }