mm/util.c: fix strndup_user() comment

The kerneldoc misdescribes strndup_user()'s return value.

Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Timur Tabi <timur@freescale.com>
Cc: Mihai Caraman <mihai.caraman@freescale.com>
Cc: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/util.c

@@ -204,7 +204,7 @@ EXPORT_SYMBOL(vmemdup_user);
  * @s: The string to duplicate
  * @n: Maximum number of bytes to copy, including the trailing NUL.
  *
- * Return: newly allocated copy of @s or %NULL in case of error
+ * Return: newly allocated copy of @s or an ERR_PTR() in case of error
  */
 char *strndup_user(const char __user *s, long n)
 {