mm/page_alloc.c: fix kernel-doc warning

Add description of function parameter 'mt' to fix kernel-doc warning:

  mm/page_alloc.c:3246: warning: Function parameter or member 'mt' not described in '__putback_isolated_page'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Link: http://lkml.kernel.org/r/02998bd4-0b82-2f15-2570-f86130304d1e@infradead.orgSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page_alloc.c

@@ -3224,6 +3224,7 @@ int __isolate_free_page(struct page *page, unsigned int order)
  * __putback_isolated_page - Return a now-isolated page back where we got it
  * @page: Page that was isolated
  * @order: Order of the isolated page
+ * @mt: The page's pageblock's migratetype
  *
  * This function is meant to return a page pulled from the free lists via
  * __isolate_free_page back to the free lists they were pulled from.