CLEANUP: peers: fix format string for status messages (int signedness)

In issue #1939, Ilya mentions that cppchecks warned about use of "%d" to
report the status state that's locally stored as an unsigned int. While
technically valid, this will never cause any trouble since in the end
what we store there are the applet's states (just a few enum values).
Better use %u anyway to silence this warning.

src/peers.c

@@ -616,7 +616,7 @@ static int peer_prepare_status_errormsg(char *msg, size_t size, struct peer_prep
 	unsigned int st1;
 
 	st1 = p->error_status.st1;
-	ret = snprintf(msg, size, "%d\n", st1);
+	ret = snprintf(msg, size, "%u\n", st1);
 	if (ret >= size)
 		return 0;