MAINTAINERS: Add myself as SPI NOR co-maintainer

I have been reviewing patches and contributing for over a year. I would
like to help maintain the subsystem as well.
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Richard Weinberger <richard@nod.at>
Link: https://lore.kernel.org/r/20211029181157.20623-1-p.yadav@ti.com

MAINTAINERS

@@ -17930,8 +17930,8 @@ F:	drivers/pinctrl/spear/
 
 SPI NOR SUBSYSTEM
 M:	Tudor Ambarus <tudor.ambarus@microchip.com>
+M:	Pratyush Yadav <p.yadav@ti.com>
 R:	Michael Walle <michael@walle.cc>
-R:	Pratyush Yadav <p.yadav@ti.com>
 L:	linux-mtd@lists.infradead.org
 S:	Maintained
 W:	http://www.linux-mtd.infradead.org/