soc: rockchip: power-domain: don't try to print the clock name in error case

When we never got the the clock-reference, i.e. when IS_ERR(clk) is true,
don't try to print the clock name via %pC as this of course produces a
null-pointer-dereference in __clk_get_name().

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Caesar Wang <wxt@rock-chips.com>