[PATCH] pinctrl: single: fix potential NULL dereference

[Tony Lindgren]

* Maxim Korotkov <korotkov.maxim.s at gmail.com> [221118 10:33]:
> Added checking of pointer "function" in pcs_set_mux().
> pinmux_generic_get_function() can return NULL and the pointer
> "function" was dereferenced without checking against NULL.

Reviewed-by: Tony Lindgren <tony at atomide.com>