mtd: rawnand: Give more information about the ECC weakness

When the ECC strength is too weak compared to the NAND chip
requirements, display the values so that it is clear for people how
much they are far from the requirements (and might get in troubles in
the future).

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200421163906.7515-1-miquel.raynal@bootlin.com