dts: arm: st: stm32wl: remove U suffix from "resets" in DTSI

STM32 reset controller position argument provided to STM32_RESET()
macro sometime uses an unnecessary U suffix. Remove these useless
suffixes for this series for consistency among STM32 SoCs DTSI files.

No functional change.

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>