mtd: do not use mtd->read_oob directly

Instead of checking whether 'mtd->read_oob' is defined, just call
'mtd_read_oob()' and handle the '-EOPNOTSUPP' error which will be returned
if the function is undefined.

Additionally, make 'mtd_write_oob()' return '-EOPNOTSUPP' if the function
is undefined.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/mtdchar.c

@@ -452,13 +452,8 @@ static int mtdchar_readoob(struct file *file, struct mtd_info *mtd,
 	if (length > 4096)
 		return -EINVAL;
 
-	if (!mtd->read_oob)
-		ret = -EOPNOTSUPP;
-	else
-		ret = access_ok(VERIFY_WRITE, ptr,
-				length) ? 0 : -EFAULT;
-	if (ret)
-		return ret;
+	if (!access_ok(VERIFY_WRITE, ptr, length))
+		return -EFAULT;
 
 	ops.ooblen = length;
 	ops.ooboffs = start & (mtd->writesize - 1);

include/linux/mtd/mtd.h

@@ -320,6 +320,8 @@ static inline int mtd_read_oob(struct mtd_info *mtd, loff_t from,
 			       struct mtd_oob_ops *ops)
 {
 	ops->retlen = ops->oobretlen = 0;
+	if (!mtd->read_oob)
+		return -EOPNOTSUPP;
 	return mtd->read_oob(mtd, from, ops);
 }
 
@@ -327,6 +329,8 @@ static inline int mtd_write_oob(struct mtd_info *mtd, loff_t to,
 				struct mtd_oob_ops *ops)
 {
 	ops->retlen = ops->oobretlen = 0;
+	if (!mtd->write_oob)
+		return -EOPNOTSUPP;
 	return mtd->write_oob(mtd, to, ops);
 }