new helper: file_inode(file)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 712b10f..90d222f 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -1625,7 +1625,7 @@
 			if (offset >= 0)
 				break;
 		default:
-			mutex_unlock(&file->f_path.dentry->d_inode->i_mutex);
+			mutex_unlock(&file_inode(file)->i_mutex);
 			return -EINVAL;
 	}
 	if (offset != file->f_pos) {