pnfs/blocklayout: fix end calculation in pnfs_num_cont_bytes

Use the number of pages in the pagecache mapping instead of the
number of pnfs requests which is only slightly related.

Reported-by: Weston Andros Adamson <dros@primarydata.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/blocklayout/blocklayout.c b/fs/nfs/blocklayout/blocklayout.c
index 4f46f7a..77fec6a 100644
--- a/fs/nfs/blocklayout/blocklayout.c
+++ b/fs/nfs/blocklayout/blocklayout.c
@@ -812,7 +812,7 @@
 
 	/* Optimize common case that writes from 0 to end of file */
 	end = DIV_ROUND_UP(i_size_read(inode), PAGE_CACHE_SIZE);
-	if (end != NFS_I(inode)->npages) {
+	if (end != inode->i_mapping->nrpages) {
 		rcu_read_lock();
 		end = page_cache_next_hole(mapping, idx + 1, ULONG_MAX);
 		rcu_read_unlock();