pnfs/blocklayout: include vmalloc.h for __vmalloc

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/blocklayout/extent_tree.c

@@ -2,6 +2,8 @@
  * Copyright (c) 2014 Christoph Hellwig.
  */
 
+#include <linux/vmalloc.h>
+
 #include "blocklayout.h"
 
 #define NFSDBG_FACILITY		NFSDBG_PNFS_LD