mm: remove return value of putback_lru_pages()

mm: remove return value of putback_lru_pages()

putback_lru_page() never can fail.  So it doesn't matter count of "the
number of pages put back".

In addition, users of this functions don't use return value.

Let's remove unnecessary code.

Signed-off-by: Minchan Kim <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Reviewed-by: KOSAKI Motohiro <[email protected]>
Reviewed-by: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>