pinctrl: ma35: Use int type to store negative error codes

Change the 'ret' variable in ma35_pinctrl_parse_functions() from u32 to
int, as it needs to store either negative error codes or zero returned
by ma35_pinctrl_parse_groups().

No effect on runtime.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>