Fix submodule force. Fixes #3490.

Makefile

@@ -109,7 +109,7 @@ endif
 # describe how to build a cmake config
 define cmake-build
 +@if [ $(PX4_CMAKE_GENERATOR) = "Ninja" ] && [ -e $(PWD)/build_$@/Makefile ]; then rm -rf $(PWD)/build_$@; fi
-+@if [ ! -e $(PWD)/build_$@/CMakeCache.txt ]; then git submodule update --init --recursive --force && mkdir -p $(PWD)/build_$@ && cd $(PWD)/build_$@ && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1); fi
++@if [ ! -e $(PWD)/build_$@/CMakeCache.txt ]; then mkdir -p $(PWD)/build_$@ && cd $(PWD)/build_$@ && cmake .. -G$(PX4_CMAKE_GENERATOR) -DCONFIG=$(1); fi
 +$(PX4_MAKE) -C $(PWD)/build_$@ $(PX4_MAKE_ARGS) $(ARGS)
 endef