arm64: dts: rockchip: drop obsolete reset-names from rk356x rng node

The reset-names property is not part of the binding, so drop it.
It is also not used by the driver, so that property was likely
a leftover from some vendor-kernel node.

Fixes: afeccc40 ("arm64: dts: rockchip: add DT entry for RNG to RK356x")
Reported-by: Rob Herring <robh@kernel.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20240815162519.751193-1-heiko@sntech.de