SITL: disable missing initializer warnings

not specifying all initializers is normal

mk/board_avr_sitl.mk

@@ -9,7 +9,7 @@ DEFINES         =   -DF_CPU=$(F_CPU)
 DEFINES        +=   -DSKETCH=\"$(SKETCH)\" -DSKETCHNAME="\"$(SKETCH)\"" -DAPM_BUILD_DIRECTORY=APM_BUILD_$(SKETCH)
 DEFINES        +=   $(EXTRAFLAGS) # from user config.mk
 DEFINES        +=   -DCONFIG_HAL_BOARD=$(HAL_BOARD)
-WARNFLAGS       =   -Wformat -Wall -Wshadow -Wpointer-arith -Wcast-align -Wno-unused-parameter
+WARNFLAGS       =   -Wformat -Wall -Wshadow -Wpointer-arith -Wcast-align -Wno-unused-parameter -Wno-missing-field-initializers
 WARNFLAGS      +=   -Wwrite-strings -Wformat=2
 WARNFLAGSCXX    =   -Wno-reorder
 DEPFLAGS        =   -MD -MT $@