mtd: rawnand: Use nanddev_mtd_max_bad_blocks()

nanddev_mtd_max_bad_blocks() is implemented by the generic NAND layer
and is already doing what we need. Reuse this function instead of
having our own implementation.

While at it, get rid of the ->max_bb_per_die and ->blocks_per_die
fields which are now unused.

Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>