9p: migrate from sync_inode to filemap_fdatawrite_wbc

We're going to remove sync_inode, so migrate to filemap_fdatawrite_wbc
instead.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/9p/vfs_file.c

@@ -625,12 +625,7 @@ static void v9fs_mmap_vm_close(struct vm_area_struct *vma)
 	p9_debug(P9_DEBUG_VFS, "9p VMA close, %p, flushing", vma);
 
 	inode = file_inode(vma->vm_file);
-
-	if (!mapping_can_writeback(inode->i_mapping))
-		wbc.nr_to_write = 0;
-
-	might_sleep();
-	sync_inode(inode, &wbc);
+	filemap_fdatawrite_wbc(inode->i_mapping, &wbc);
 }