ARM: dts: stm32: fix -Wall W=1 compilation in stm32mp157 pinctrl for mcan

Fix compilations warnings detected by -Wall W=1 compilation option:
- node has a unit name, but no reg property
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp157-pinctrl.dtsi

@@ -574,7 +574,7 @@ pins2 {
 				};
 			};
 
-			m_can1_sleep_pins_a: m_can1-sleep@0 {
+			m_can1_sleep_pins_a: m_can1-sleep-0 {
 				pins {
 					pinmux = <STM32_PINMUX('H', 13, ANALOG)>, /* CAN1_TX */
 						 <STM32_PINMUX('I', 9, ANALOG)>; /* CAN1_RX */