macaddr: fix osmo_get_macaddr(): return -1 if no device is found

Change-Id: I74d33159485ec1f7f09b444621a2d1941c3dd4db
diff --git a/src/macaddr.c b/src/macaddr.c
index de9d07a..a9138f8 100644
--- a/src/macaddr.c
+++ b/src/macaddr.c
@@ -102,7 +102,7 @@
 	}
 
 	freeifaddrs(ifaddr);
-	return 0;
+	return rc;
 }
 
 #else