clk: rockchip: include downstream muxes into fractional dividers on rk3368

During the initial conversion to the newly introduced combined fractional
dividers+muxes the rk3368 clocks were left out, so convert them now.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>