MAINTAINERS: Update maintainers for new Documentation/litmus-tests

This commit adds Joel Fernandes as official LKMM reviewer.
Acked-by: Boqun Feng <boqun.feng@gmail.com>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Apply Joe Perches alphabetization feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

MAINTAINERS

@@ -9960,6 +9960,7 @@ M:	Luc Maranget <luc.maranget@inria.fr>
 M:	"Paul E. McKenney" <paulmck@kernel.org>
 R:	Akira Yokosawa <akiyks@gmail.com>
 R:	Daniel Lustig <dlustig@nvidia.com>
+R:	Joel Fernandes <joel@joelfernandes.org>
 L:	linux-kernel@vger.kernel.org
 L:	linux-arch@vger.kernel.org
 S:	Supported
@@ -9968,6 +9969,7 @@ F:	Documentation/atomic_bitops.txt
 F:	Documentation/atomic_t.txt
 F:	Documentation/core-api/atomic_ops.rst
 F:	Documentation/core-api/refcount-vs-atomic.rst
+F:	Documentation/litmus-tests/
 F:	Documentation/memory-barriers.txt
 F:	tools/memory-model/