ovl: rename filesystem type to "overlay"

Some distributions carry an "old" format of overlayfs while mainline has a
"new" format.

The distros will possibly want to keep the old overlayfs alongside the new
for compatibility reasons.

To make it possible to differentiate the two versions change the name of
the new one from "overlayfs" to "overlay".

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Reported-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Cc: Andy Whitcroft <apw@canonical.com>
diff --git a/MAINTAINERS b/MAINTAINERS
index c444907..af1e738 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6888,7 +6888,7 @@
 F:	include/scsi/osd_*
 F:	fs/exofs/
 
-OVERLAYFS FILESYSTEM
+OVERLAY FILESYSTEM
 M:	Miklos Szeredi <miklos@szeredi.hu>
 L:	linux-fsdevel@vger.kernel.org
 S:	Supported