mtd: rawnand: brcmnand: remove unused parameters

last_cmd and last_byte are now unused brcmnand_host members.
last_addr is only written and never read so we can remove it too.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Reviewed-by: William Zhang <william.zhang@broadcom.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>