rtc: sun6i: Fix memleak in sun6i_rtc_clk_init

When clk_hw_register_fixed_rate_with_accuracy() fails,
clk_data should be freed. It's the same for the subsequent
two error paths, but we should also unregister the already
registered clocks in them.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201020061226.6572-1-dinghao.liu@zju.edu.cn