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 <[e-mail]>
Acked-by: Miquel Raynal <[e-mail]>
Acked-by: Marek Vasut <[e-mail]>
Acked-by: Richard Weinberger <[e-mail]>
Signed-off-by: Boris Brezillon <[e-mail]>

MAINTAINERS

···
 
 SPI NOR SUBSYSTEM
 M:	Marek Vasut <[e-mail]>
+M:	Tudor Ambarus <[e-mail]>
 L:	[e-mail]
 W:	http://www.linux-mtd.infradead.org/
 Q:	http://patchwork.ozlabs.org/project/linux-mtd/list/