mtd: rawnand: tegra: check bounds of die_nr properly

The Tegra driver currently only support a single chip select, hence
check boundaries accordingly. This fixes a off by one issue catched
with Smatch:
    drivers/mtd/nand/raw/tegra_nand.c:476 tegra_nand_select_chip()
    warn: array off by one? 'nand->cs[die_nr]'

Also warn in case the stack asks for a chip select we currently do
not support.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>