cmake nuttx .px4 package fix dependency location

platforms/nuttx/CMakeLists.txt

@@ -124,9 +124,10 @@ add_custom_command(OUTPUT ${PX4_BINARY_DIR_REL}/${PX4_BOARD}.bin
 # create .px4 with parameter and airframe metadata
 if (TARGET parameters_xml AND TARGET airframes_xml)
 
-	string(REPLACE ".elf" ".px4" fw_package ${FW_NAME})
+	string(REPLACE ".elf" ".px4" fw_package ${PX4_BINARY_DIR}/${FW_NAME})
 
-	add_custom_command(OUTPUT ${fw_package}
+	add_custom_command(
+		OUTPUT ${fw_package}
 		COMMAND
 			${PYTHON_EXECUTABLE} ${PX4_SOURCE_DIR}/Tools/px_mkfw.py
 				--prototype ${PX4_SOURCE_DIR}/boards/${PX4_BOARD_VENDOR}/${PX4_BOARD_MODEL}/firmware.prototype