Add missing define for DSM

msg/input_rc.msg

@@ -10,7 +10,8 @@ uint8 RC_INPUT_SOURCE_PX4FMU_SPEKTRUM = 8
 uint8 RC_INPUT_SOURCE_PX4FMU_SBUS = 9
 uint8 RC_INPUT_SOURCE_PX4FMU_ST24 = 10
 uint8 RC_INPUT_SOURCE_PX4FMU_SUMD = 11
-uint8 RC_INPUT_SOURCE_PX4IO_SUMD = 12
+uint8 RC_INPUT_SOURCE_PX4FMU_DSM = 12
+uint8 RC_INPUT_SOURCE_PX4IO_SUMD = 13
 
 uint8 RC_INPUT_MAX_CHANNELS = 18 	# Maximum number of R/C input channels in the system. S.Bus has up to 18 channels.