mtd: nand: Rename the nand_manufacturers struct

Upstream linux commit 8cfb9ab68f9070.

Drop the 's' at the end of nand_manufacturers since the struct is actually
describing a single manufacturer, not a manufacturer table.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>