mtd: nand: correct extemded param page error handling

If the ONFI extended parameter page gives codeword_size == 0, the
extended ECC information is corrupt and should not be used. Currently,
we (correctly) avoid using the information, but we don't report the
error to the caller, so the caller doesn't know that we didn't
initialize ecc_strength_ds and ecc_step_ds. Now the caller can warn the
user that it does not have sufficient information.

This also removes the false and useless "ONFI extended param page
detected" debug message (it was printed even on the aforementioned
corruption, and for the success case, we don't really want a print).

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Huang Shijie <b32955@freescale.com>