NFS: use size_t type for holding rsize bytes in NFS O_DIRECT read path

size_t is used for holding byte counts, so use it for variables storing rsize.
Note that the write path will be updated as we add support for async
O_DIRECT writes.

Test plan:
Need to verify that existing comparisons against new size_t variables behave
correctly.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/direct.c

@@ -161,7 +161,7 @@ static void nfs_direct_req_release(struct kref *kref)
  * done.  This prevents races with I/O completion so we will always wait
  * until all requests have been dispatched and completed.
  */
-static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, unsigned int rsize)
+static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, size_t rsize)
 {
 	struct list_head *list;
 	struct nfs_direct_req *dreq;
@@ -244,14 +244,14 @@ static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, struct inode *
 {
 	struct list_head *list = &dreq->list;
 	struct page **pages = dreq->pages;
+	size_t rsize = NFS_SERVER(inode)->rsize;
 	unsigned int curpage, pgbase;
-	unsigned int rsize = NFS_SERVER(inode)->rsize;
 
 	curpage = 0;
 	pgbase = user_addr & ~PAGE_MASK;
 	do {
 		struct nfs_read_data *data;
-		unsigned int bytes;
+		size_t bytes;
 
 		bytes = rsize;
 		if (count < rsize)