dt-bindings: clock: rk3568: Drop CLK_NR_CLKS define

CLK_NR_CLKS has always only be used on the driver side to calculate array
sizes should never have been part of the clock-binding.

Let's drop it, since the kernel code no longer uses it either and nothing
else has ever used it.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20251103234032.413563-3-heiko@sntech.de