MAINTAINERS: Add myself as MTD maintainer

Help Richard and hopefully Tudor and Vignesh maintaining MTD since
Boris is leaving.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

MAINTAINERS

@@ -10009,6 +10009,7 @@ MEMORY TECHNOLOGY DEVICES (MTD)
 M:	David Woodhouse <dwmw2@infradead.org>
 M:	Brian Norris <computersforpeace@gmail.com>
 M:	Marek Vasut <marek.vasut@gmail.com>
+M:	Miquel Raynal <miquel.raynal@bootlin.com>
 M:	Richard Weinberger <richard@nod.at>
 M:	Vignesh Raghavendra <vigneshr@ti.com>
 L:	linux-mtd@lists.infradead.org