MAINTAINERS: Rename NAND FLASH to RAW NAND

As there are other types of NAND flashes like SPI NAND, let's be
more specific.

Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Link: https://lore.kernel.org/all/20230213094626.50957-2-frieder@fris.de/


Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>