NuttX shell scripts: replace operator == with =

- NuttX supports both versions
- POSIX shell only supports '='

ROMFS/px4fmu_test/init.d/rc.sensors

@@ -46,7 +46,7 @@ then
 		set BOARD_FMUV3 false
 	fi
 
-	if [ $BOARD_FMUV3 == true ]
+	if [ $BOARD_FMUV3 = true ]
 	then
 		# external L3GD20H is rotated 180 degrees yaw
 		if l3gd20 -X -R 4 start

ROMFS/px4fmu_test/init.d/rcS

@@ -24,7 +24,7 @@ fi
 # Try to mount the microSD card.
 #
 mount -t vfat /dev/mmcsd0 /fs/microsd
-if [ $? == 0 ]
+if [ $? = 0 ]
 then
 	echo "[i] card mounted at /fs/microsd"
 	# Start playing the startup tune