pinctrl: sunxi: fix error return code in sunxi_pinctrl_probe()

Fix to return a negative error code from the devm_clk_get() error
handling case instead of 0, as done elsewhere in this function.

Introduced by commit 950707c0
(pinctrl: sunxi: add clock support)

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>