libmount: mark overlay as pseudo-FS

Signed-off-by: Karel Zak <kzak@redhat.com>
diff --git a/libmount/src/utils.c b/libmount/src/utils.c
index bc43a85..332f515 100644
--- a/libmount/src/utils.c
+++ b/libmount/src/utils.c
@@ -271,6 +271,7 @@
 		"mqueue",
 		"nfsd",
 		"none",
+		"overlay",
 		"pipefs",
 		"proc",
 		"pstore",