MAINTAINERS: Add myself as co-maintainer for MTD

I have been contributing and reviewing MTD patches for a while now and
would like to add myself as co-maintainer for MTD to help maintain
CFI and SPI NOR parts of the subsystem.
Hopefully, this will help in taking some load off current maintainers.
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

MAINTAINERS

@@ -10011,6 +10011,7 @@ M:	Brian Norris <computersforpeace@gmail.com>
 M:	Boris Brezillon <bbrezillon@kernel.org>
 M:	Marek Vasut <marek.vasut@gmail.com>
 M:	Richard Weinberger <richard@nod.at>
+M:	Vignesh Raghavendra <vigneshr@ti.com>
 L:	linux-mtd@lists.infradead.org
 W:	http://www.linux-mtd.infradead.org/
 Q:	http://patchwork.ozlabs.org/project/linux-mtd/list/