MAINTAINERS: add myself as SPI NOR co-maintainer

I have been reviewing and contributing to the SPI NOR subsystem
for the last few months and I'm willing to continue doing so.
Volunteer as a maintainer for the SPI NOR part of the MTD subsystem.
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>

MAINTAINERS

@@ -14303,6 +14303,7 @@ F:	arch/arm/mach-spear/
 
 SPI NOR SUBSYSTEM
 M:	Marek Vasut <marek.vasut@gmail.com>
+M:	Tudor Ambarus <tudor.ambarus@microchip.com>
 L:	linux-mtd@lists.infradead.org
 W:	http://www.linux-mtd.infradead.org/
 Q:	http://patchwork.ozlabs.org/project/linux-mtd/list/