mm/swapfile.c: make pointer swap_avail_heads static

The pointer swap_avail_heads is local to the source and does not need to
be in global scope, so make it static.

Cleans up sparse warning:

  mm/swapfile.c:88:19: warning: symbol 'swap_avail_heads' was not declared. Should it be static?

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Colin Ian King <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Acked-by: "Huang, Ying" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index a134d1e..cc2cf04 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -85,7 +85,7 @@ PLIST_HEAD(swap_active_head);
  * is held and the locking order requires swap_lock to be taken
  * before any swap_info_struct->lock.
  */
-struct plist_head *swap_avail_heads;
+static struct plist_head *swap_avail_heads;
 static DEFINE_SPINLOCK(swap_avail_lock);
 
 struct swap_info_struct *swap_info[MAX_SWAPFILES];