dt-bindings: clocks: Fix typo in the H6 compatible

Even though both the driver and the device trees all use the
allwinner,sun50i-h6-de3-clk, we documented the compatible as
allwinner,sun50i-h6-de2-clk in the binding. Let's fix this.

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20210901091852.479202-10-maxime@cerno.tech