fixing all "argc < 1" to avoid segmentation fault when calling the module with no parameters

argc is never smaller than one because the first element of the array is the program name!

src/modules/ekf2/ekf2_main.cpp

@@ -751,7 +751,7 @@ int Ekf2::start()
 
 int ekf2_main(int argc, char *argv[])
 {
-	if (argc < 1) {
+	if (argc < 2) {
 		PX4_WARN("usage: ekf2 {start|stop|status}");
 		return 1;
 	}