mtd: nand: remove unnecessary TODO

I believe this TODO was unnecessary back when it was introduced:
	commit d1e1f4e4
	mtd: nand: add support for reading ONFI parameters...

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>