ovl: add Amir as co-maintainer

Amir has implemented lots of features in overlayfs and is very active in
maintenance.

Make this official in the MAINTAINERS file.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

MAINTAINERS

@@ -15846,6 +15846,7 @@ F:	include/media/i2c/ov2659.h
 
 OVERLAY FILESYSTEM
 M:	Miklos Szeredi <miklos@szeredi.hu>
+M:	Amir Goldstein <amir73il@gmail.com>
 L:	linux-unionfs@vger.kernel.org
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git