mtd: rawnand: sunxi: replace hard coded value by a define - take2

mtd: rawnand: sunxi: replace hard coded value by a define - take2

The user data length (4) has been replaced almost all over the file, but
2 places were forgotten.

The user data is placed before the ECC, for each step.
So, in sunxi_nfc_hw_ecc_read_extra_oob(), the offset of the user data in
OOB is indeed ((ecc->bytes + USER_DATA_SZ) * ecc->steps);

And in sunxi_nand_ooblayout_ecc(), the offset of the ECC chunk in OOB is
the same offset plus the current user data size:
section * (ecc->bytes + USER_DATA_SZ) + USER_DATA_SZ;

Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Richard Genoud <richard.genoud@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>