mtd: nand: samsung: warn about un-parseable ECC info

We don't handle cases larger than 7. We probably shouldn't pretend we
know the ECC step size in this case, and it's probably also good to
WARN() like we do in many other similar cases.

Fixes: 8fc82d45 ("mtd: nand: samsung: Retrieve ECC requirements from extended ID")
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>