build: fix NuttX menuconfig

There was and extra "nuttx" dir:
	cp: cannot stat '/home/lucas/p/dronecode/PX4/Firmware/build/aerofc-v1_default/NuttX/nuttx/nuttx/.config': No such file or directory
	FAILED: NuttX/CMakeFiles/menuconfig

And the board fixup being executed from the wrong working directory:
	nuttx-configs/aerofc-v1/nsh/defconfig
	fatal: Path 'nuttx-configs/aerofc-v1/nsh/defconfig' does not exist in 'HEAD'

platforms/nuttx/NuttX/CMakeLists.txt

@@ -203,8 +203,8 @@ add_custom_target(oldconfig
 # menuconfig helper
 add_custom_target(menuconfig
 	COMMAND make --no-print-directory --silent -C ${NUTTX_DIR} CONFIG_ARCH_BOARD=${BOARD} menuconfig
-	COMMAND cp ${NUTTX_DIR}/nuttx/.config ${NUTTX_CONFIG_DIR}/${BOARD}/${nuttx_config_type}/defconfig
-	COMMAND ${PX4_SOURCE_DIR}/platforms/nuttx/NuttX/tools/nuttx_defconf_tool.sh ${NUTTX_CONFIG_DIR}/${BOARD}/${nuttx_config_type}/defconfig
+	COMMAND cp ${NUTTX_DIR}/.config ${NUTTX_CONFIG_DIR}/${BOARD}/${nuttx_config_type}/defconfig
+	COMMAND cd ${PX4_SOURCE_DIR} && platforms/nuttx/NuttX/tools/nuttx_defconf_tool.sh ${NUTTX_CONFIG_DIR}/${BOARD}/${nuttx_config_type}/defconfig
 	DEPENDS nuttx_configure
 	WORKING_DIRECTORY ${NUTTX_DIR}
 	COMMENT "Running NuttX make menuconfig for ${BOARD} with ${nuttx_config_type}"