mtd: vf610_nfc: allow bitflips in an empty page

Allow bit flips in a empty page up to half of the recoverable
bits (strength / 2).

Signed-off-by: Stefan Agner <stefan@agner.ch>
diff --git a/drivers/mtd/nand/vf610_nfc.c b/drivers/mtd/nand/vf610_nfc.c
index 66b335d..16485f5 100644
--- a/drivers/mtd/nand/vf610_nfc.c
+++ b/drivers/mtd/nand/vf610_nfc.c
@@ -527,7 +527,7 @@
 	flip = count_written_bits(dat, nfc->chip.ecc.size, ecc_count);
 
 	/* ECC failed. */
-	if (flip > ecc_count)
+	if (flip > ecc_count && flip > (nfc->chip.ecc.strength / 2))
 		return -1;
 
 	/* Erased page. */