mtd: rawnand: marvell: remove bogus comment in marvell_nfc_select_chip()

The comment in marvell_nfc_select_chip() about ndtr0 and ndtr1 didn't
reflect what the driver was doing.

The values of NDTR0 and NDTR1 are read from the registers at probe time
and a copy is retained in 'struct marvell_nand_chip'. If keep-config is
set in the DT properties, there are no other writers of these timing
variables so they can safely be used when the chip is selected.

As suggested by Miquel Raynal, simply remove the comment.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>