Fix va_arg calls (always call va_end)

From the manpage: "Each invocation of va_start() must be matched by a
corresponding invocation of va_end() in the same function."

src/examples/ekf_att_pos_estimator/estimator_utilities.cpp

@@ -64,6 +64,7 @@ ekf_debug(const char *fmt, ...)
 
     va_start(args, fmt);
     ekf_debug_print(fmt, args);
+    va_end(args);
 }
 
 #else