ARM: dts: stm32: fix i2c node name on stm32f746 to prevent warnings

Replace upper case by lower case in i2c nodes name.
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32f746.dtsi

@@ -360,9 +360,9 @@ i2c2: i2c@40005800 {
 			status = "disabled";
 		};
 
-		i2c3: i2c@40005C00 {
+		i2c3: i2c@40005c00 {
 			compatible = "st,stm32f7-i2c";
-			reg = <0x40005C00 0x400>;
+			reg = <0x40005c00 0x400>;
 			interrupts = <72>,
 				     <73>;
 			resets = <&rcc STM32F7_APB1_RESET(I2C3)>;