mtd: rawnand: brcmnand: Fix ecc chunk calculation for erased page bitfips

In brcmstb_nand_verify_erased_page(), the ECC chunk pointer calculation
while correcting erased page bitflips is wrong, fix it.

Fixes: 02b88eea ("mtd: brcmnand: Add check for erased page bitflips")
Signed-off-by: Claire Lin <claire.lin@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>