clk: rockchip: free memory in error cases when registering clock branches

Add free memeory if rockchip_clk_register_branch fails.

Fixes: a245fecb ("clk: rockchip: add basic infrastructure...")
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>