pinctrl: pinctrl_stm32: Use GPIOF_UNKNOWN to indicate not mapped pins

GPIOF_UNKNOWN becomes a valid pin muxing information to indicate
that a pin is not mapped.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
1 file changed