drm/vc4: Fix memory leak of the CRTC state.

The underscores variant frees the pointers inside, while the
no-underscores variant calls underscores and then frees the struct.

Signed-off-by: Eric Anholt <eric@anholt.net>
Fixes: d8dbf44f ("drm/vc4: Make the CRTCs cooperate on allocating display lists.")
Cc: stable@vger.kernel.org