boards: nxp: add mikrobus_i2c to lpcxpresso55s69

This was missing despite other mikrobus labels being there. Verified
against LPCXpresso55S69_Board_Schematic_RevA2_dec4.pdf

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

boards/nxp/lpcxpresso55s69/lpcxpresso55s69.dtsi

@@ -179,6 +179,9 @@ mikrobus_serial: &flexcomm2 {
 mikrobus_spi: &hs_lspi {
 };
 
+mikrobus_i2c: &flexcomm4 {
+};
+
 &flexcomm0 {
 	pinctrl-0 = <&pinmux_flexcomm0_usart>;
 	pinctrl-names = "default";