clk: rockchip: Remove superfluous error message in rockchip_clk_register_cpuclk()

Omit an extra message for a memory allocation failure in this function.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>