mtd: nand: sunxi: fix bitflips in erased pages

Use the nand_check_erased_ecc_chunk() function to test if the ECC error
was triggered by an erased page containing a few bitflips.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>