MAINTAINERS: drop Wenyou Yang from Atmel NAND driver support

Mails to wenyou.yang@microchip.com are not deliverable.
Drop him as Microchip/Atmel NAND controller driver maintainer.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>