mission_block: swapped "param6" for "altitude" for consistency

src/modules/navigator/mission_block.cpp

@@ -456,7 +456,7 @@ MissionBlock::issue_command(const mission_item_s &item)
 		if (item.nav_cmd == NAV_CMD_DO_SET_ROI_LOCATION && item.altitude_is_relative) {
 			vcmd.param5 = item.lat;
 			vcmd.param6 = item.lon;
-			vcmd.param7 = item.params[6] + _navigator->get_home_position()->alt;
+			vcmd.param7 = item.altitude + _navigator->get_home_position()->alt;
 
 		} else {
 			vcmd.param5 = item.params[4];