clk: rockchip: rk3368: fix cpuclk mux bit of big cpu-cluster

Both clusters have their mux bit in bit 7 of their respective register.
For whatever reason the big cluster currently lists bit 15 which is
definitly wrong.

Fixes: 3536c97a ("clk: rockchip: add rk3368 clock controller")
Reported-by: Zhang Qing <zhangqing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: zhangqing <zhangqing@rock-chips.com>
Cc: stable@vger.kernel.org