dt-bindings: mtd: gpmc: Fix the ECC bytes vs. OOB bytes equation

dt-bindings: mtd: gpmc: Fix the ECC bytes vs. OOB bytes equation

"PAGESIZE / 512" is the number of ECC chunks.
"ECC_BYTES" is the number of bytes needed to store a single ECC code.
"2" is the space reserved by the bad block marker.

"2 + (PAGESIZE / 512) * ECC_BYTES" should of course be lower or equal
than the total number of OOB bytes, otherwise it won't fit.

Fix the equation by substituting s/>=/<=/.

Suggested-by: Ryan J. Barnett <ryan.barnett@collins.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20210610143945.3504781-1-miquel.raynal@bootlin.com