dts/bindings: stm32-otg: Set pinctrl-[0/names] properties as required

Follow up on commit 37bf7cbe
("dts/bindings: stm32: Set pinctrl-[0/names] properties as required")
Report lack of those fields soon at build to avoid cryptic
DT api build error messages.

Signed-off-by: Maciej Zagrabski <maciej.zagrabski@grinn-global.com>