mtdblock: tolerate corrected bit-flips

mtd_read() may return -EUCLEAN in case of corrected bit-flips.This
particular condition should not be treated like an error.

Signed-off-by: Bang Li <libang.linuxer@gmail.com>
Fixes: e47f6858 ("mtd: check for max_bitflips in mtd_read_oob()")
Cc: <stable@vger.kernel.org> # v3.7
Acked-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230328163012.4264-1-libang.linuxer@gmail.com