pinctrl: protect pinctrl_list add

pinctrl: protect pinctrl_list add

We have few fedora bug reports about list corruption on pinctrl,
for example:
https://bugzilla.redhat.com/show_bug.cgi?id=1051918

Most likely corruption happen due lack of protection of pinctrl_list
when adding new nodes to it. Patch corrects that.

Fixes: 42fed7ba44e ("pinctrl: move subsystem mutex to pinctrl_dev struct")
Cc: [email protected]
Signed-off-by: Stanislaw Gruszka <[email protected]>
Acked-by: Stephen Warren <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>