dt-bindings: clk: vc5: Fix example

The example properties do not match the binding. Fix them, and prohibit
undocumented properties in clock nodes to prevent this from happening in
the future.

Fixes: 45c94018 ("dt-bindings: clk: versaclock5: convert to yaml")
Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Link: https://lore.kernel.org/r/20210607190546.2616259-1-sean.anderson@seco.com


Signed-off-by: Rob Herring <robh@kernel.org>