pinctrl: single: Fix incorrect type for error return variable

pinctrl: single: Fix incorrect type for error return variable

pcs_pinconf_get() and pcs_pinconf_set() declare ret as unsigned int,
but assign it the return values of pcs_get_function() that may return
negative error codes. This causes negative error codes to be
converted to large positive values.

Change ret from unsigned int to int in both functions.

Fixes: 9dddb4df90d1 ("pinctrl: single: support generic pinconf")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Signed-off-by: Linus Walleij <linusw@kernel.org>