INAV: Valgrind fix

Make sure `struct position_estimator_inav_params params` is properly initialized.

At first there was no indication that this struct was un-initialized because valgrind
was issuing warnings about values that were derived (via float calculations) from
values in this struct. Maybe instruction re-ordering during optimization caused
this disconnect between the source of the problem and the symptom.

src/modules/position_estimator_inav/position_estimator_inav_main.c

@@ -380,6 +380,7 @@ int position_estimator_inav_thread_main(int argc, char *argv[])
 	orb_advert_t vehicle_global_position_pub = NULL;
 
 	struct position_estimator_inav_params params;
+	memset(&params, 0, sizeof(params));
 	struct position_estimator_inav_param_handles pos_inav_param_handles;
 	/* initialize parameter handles */
 	inav_parameters_init(&pos_inav_param_handles);