NFS: Prevent integer overflow in nfs_scan_list()

Also ensure that nfs_inode ncommit and npages are large enough to represent
all possible values for the number of pages.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index ad90cbe..68f6bf1 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -425,6 +425,8 @@
 						req->wb_index, tag);
 				nfs_list_add_request(req, dst);
 				res++;
+				if (res == INT_MAX)
+					goto out;
 			}
 		}