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/platforms/qurt/px4_layer/px4_qurt_impl.cpp

@@ -80,6 +80,7 @@ void qurt_log(const char *fmt, ...)
 	va_start(args, fmt);
 	printf(fmt, args);
 	printf("n");
+	va_end(args);
 }
 #endif