Do not include linux/backing-dev.h twice

Don't include linux/backing-dev.h twice in mm/filemap.c, it's pointless.

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/filemap.c b/mm/filemap.c
index 5c74b68..ab98557 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -28,7 +28,6 @@
 #include <linux/backing-dev.h>
 #include <linux/pagevec.h>
 #include <linux/blkdev.h>
-#include <linux/backing-dev.h>
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/cpuset.h>