clk: rockchip: fix cpuclk registration error handling

It maybe due to a copy-paste error the error handing should be
cclk not clk when checking if the cpuclk registration succeeded.

Reported-by: Lin Huang <lin.huang@rock-chips.com>
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>