pinctrl: pinmux: handle radix_tree_insert() errors in pinmux_generic_add_function()

pinctrl_generic_add_function() doesn't check result of radix_tree_insert()
despite they both may return a negative error code.  Linus Walleij said he
has copied the radix tree code from kernel/irq/ where the functions calling
radix_tree_insert() are *void* themselves; I think it makes more sense to
propagate the errors from radix_tree_insert() upstream if we can do that...

Found by Linux Verification Center (linuxtesting.org) with the Svace static
analysis tool.

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Link: https://lore.kernel.org/r/20230719202253.13469-4-s.shtylyov@omp.ru
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Author: Sergey Shtylyov

drivers/pinctrl/pinmux.c

@@ -872,7 +872,7 @@ int pinmux_generic_add_function(struct pinctrl_dev *pctldev,
 				void *data)
 {
 	struct function_desc *function;
-	int selector;
+	int selector, error;
 
 	if (!name)
 		return -EINVAL;
@@ -892,7 +892,9 @@ int pinmux_generic_add_function(struct pinctrl_dev *pctldev,
 	function->num_group_names = num_groups;
 	function->data = data;
 
-	radix_tree_insert(&pctldev->pin_function_tree, selector, function);
+	error = radix_tree_insert(&pctldev->pin_function_tree, selector, function);
+	if (error)
+		return error;
 
 	pctldev->num_functions++;