MAINTAINERS: add more people to the MTD maintainer team

Brian has been maintaining the MTD subsystem alone for several years
now, and maintaining such a subsystem can really be time consuming.

Create a maintainer team formed of the most active MTD contributors
to help Brian with this task, which will hopefully improve the
subsystem reactivity.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

Author: Boris Brezillon

MAINTAINERS

@@ -7912,6 +7912,10 @@ F:	mm/
 MEMORY TECHNOLOGY DEVICES (MTD)
 M:	David Woodhouse <dwmw2@infradead.org>
 M:	Brian Norris <computersforpeace@gmail.com>
+M:	Boris Brezillon <boris.brezillon@free-electrons.com>
+M:	Marek Vasut <marek.vasut@gmail.com>
+M:	Richard Weinberger <richard@nod.at>
+M:	Cyrille Pitchen <cyrille.pitchen@atmel.com>
 L:	linux-mtd@lists.infradead.org
 W:	http://www.linux-mtd.infradead.org/
 Q:	http://patchwork.ozlabs.org/project/linux-mtd/list/