fix OOB size decoding on SK Hynix H27UCG8T2BTR

The OOB size of the SK Hynix H27UCG8T2BTR is currently detected to be 640 bytes, while the datasheet states that it should be 1280 bytes.

I only have one single device with a SK Hynix NAND flash, so I cannot say whether this fix may or may not break other chips. other datasheets I have checked:
- H27UBG8T2B uses a page size of 8KiB -> not applicable
- H27UBG8T2A also uses a page size of 8KiB -> not applicable either

so I would appreciate if someone else could confirm (even if it's "just" by looking at a datasheet) that this patch should work for other SK Hynix NAND chips with 16KiB page size.

I decided not to add a "Fixes" tag because it seems H27UCG8T2BTR was not supported properly at any point in the past (upstream at least).

changes since v1 at [0]:
- don't apply the fix for all Hynix chips with 16KiB page size as suggested by Miquel Raynal
- added an inline comment what the new logic is supposed to do
- I asked Hynix for feedback on my initial patch, unfortunately it seems that they cannot disclose any information from the datasheets publicly

[0] https://patchwork.ozlabs.org/cover/916836/

Martin Blumenstingl (1):
mtd: rawnand: hynix: fix decoding the OOB size on H27UCG8T2BTR

 drivers/mtd/nand/raw/nand_hynix.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)