fs: nfs: Adding new return type vm_fault_t

Use new return type vm_fault_t for fault handler
in struct vm_operations_struct. For now, this is
just documenting that the function returns a
VM_FAULT value rather than an errno.  Once all
instances are converted, vm_fault_t will become
a distinct type.

see commit 1c8f4220 ("mm: change return type to
vm_fault_t") for reference.
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/file.c

@@ -532,13 +532,13 @@ const struct address_space_operations nfs_file_aops = {
  * writable, implying that someone is about to modify the page through a
  * shared-writable mapping
  */
-static int nfs_vm_page_mkwrite(struct vm_fault *vmf)
+static vm_fault_t nfs_vm_page_mkwrite(struct vm_fault *vmf)
 {
 	struct page *page = vmf->page;
 	struct file *filp = vmf->vma->vm_file;
 	struct inode *inode = file_inode(filp);
 	unsigned pagelen;
-	int ret = VM_FAULT_NOPAGE;
+	vm_fault_t ret = VM_FAULT_NOPAGE;
 	struct address_space *mapping;
 
 	dfprintk(PAGECACHE, "NFS: vm_page_mkwrite(%pD2(%lu), offset %lld)\n",