clk-sunxi: fix a missing-check bug in sunxi_divs_clk_setup()

mainline inclusion
from mainline-v5.3
commit fcdf445f
category: bugfix
bugzilla: 13690
CVE: CVE-2019-12455

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In sunxi_divs_clk_setup(), 'derived_name' is allocated by kstrndup().
It returns NULL when fails. 'derived_name' should be checked.

Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>