mtd: rawnand: txx9ndfmc: rename nand controller internal structure

As already done in the core, calling a struct nand_controller
'hw_control' is misleading. Use the same name as in nand_base.c:
'controller'.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>