mm: don't include <linux/blk-cgroup.h> in <linux/backing-dev.h>

There is no need to pull blk-cgroup.h and thus blkdev.h in here, so
break the include chain.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Johannes Thumshirn <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 22d10f7..30db362 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -18,7 +18,7 @@
 #include <linux/pagemap.h>
 #include <linux/namei.h>
 #include <linux/shmem_fs.h>
-#include <linux/blkdev.h>
+#include <linux/blk-cgroup.h>
 #include <linux/random.h>
 #include <linux/writeback.h>
 #include <linux/proc_fs.h>