mtd: nand: ecc-bch: Return only valid error codes

When a function is not available, returning -ENOTSUPP makes much more
sense than returning -1.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200929230124.31491-6-miquel.raynal@bootlin.com

include/linux/mtd/nand-ecc-sw-bch.h

@@ -43,7 +43,7 @@ static inline int
 nand_bch_calculate_ecc(struct nand_chip *chip, const u_char *dat,
 		       u_char *ecc_code)
 {
-	return -1;
+	return -ENOTSUPP;
 }
 
 static inline int