Hardware ECC does not work for erased pages. However as soon as
something that is not 0xff is found in the page, hardware ECC assumes
this is valid data and produces an uncorrectable error ECC status. We
can use that to check for bitflips in erased pages and fix them if the
number of flipped bits is below the ecc_strength.

We need to move the memcpy above the for loop to be able to access the
buffer directly.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>