mtd: do not use mtd->lock_user_prot_reg directly

Instead, check the -EOPNOTSUPP return code of 'mtd_lock_user_prot_reg()'.

Signed-off-by: Artem Bityutskiy <[e-mail]>
Signed-off-by: David Woodhouse <[e-mail]>

drivers/mtd/mtdchar.c

···
 			return -EINVAL;
 		if (copy_from_user(&oinfo, argp, sizeof(oinfo)))
 			return -EFAULT;
-		if (!mtd->lock_user_prot_reg)
-			return -EOPNOTSUPP;
 		ret = mtd_lock_user_prot_reg(mtd, oinfo.start, oinfo.length);
 		break;
 	}

include/linux/mtd/mtd.h

···
 static inline int mtd_lock_user_prot_reg(struct mtd_info *mtd, loff_t from,
 					 size_t len)
 {
+	if (!mtd->lock_user_prot_reg)
+		return -EOPNOTSUPP;
 	return mtd->lock_user_prot_reg(mtd, from, len);
 }