lib/idr.c: fix comment for idr_replace()

idr_replace() returns the old value on success, not 0.

Link: http://lkml.kernel.org/r/20170918162642.37511-1-ebiggers3@gmail.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/idr.c

@@ -146,8 +146,8 @@ EXPORT_SYMBOL(idr_get_next_ext);
  * idr_alloc() and idr_remove() (as long as the ID being removed is not
  * the one being replaced!).
  *
- * Returns: 0 on success.  %-ENOENT indicates that @id was not found.
- * %-EINVAL indicates that @id or @ptr were not valid.
+ * Returns: the old value on success.  %-ENOENT indicates that @id was not
+ * found.  %-EINVAL indicates that @id or @ptr were not valid.
  */
 void *idr_replace(struct idr *idr, void *ptr, int id)
 {