ARM: dts: sun8i: v3s: Remove redundant assigned-clocks

The V3s mixer node has an assigned clocks property, while the driver also
enforces it.

Since assigned-clocks is pretty fragile anyway, let's just remove it.

Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>