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>

fs/nfs/pagelist.c

@@ -425,6 +425,8 @@ int nfs_scan_list(struct nfs_inode *nfsi,
 						req->wb_index, tag);
 				nfs_list_add_request(req, dst);
 				res++;
+				if (res == INT_MAX)
+					goto out;
 			}
 		}