clk: mvebu/clk-cpu.c: fix memory leakage

the variable cpuclk and clk_name should be properly freed when error happens.

Signed-off-by: Cong Ding <dinggnu@gmail.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Acked-by: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>