new helper: file_inode(file)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 78e2ecb..c057104 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -251,7 +251,7 @@
 		return PTR_ERR(file);
 
 	err = -EINVAL;
-	ei = PROC_I(file->f_dentry->d_inode);
+	ei = PROC_I(file_inode(file));
 	ops = ei->ns_ops;
 	if (nstype && (ops->type != nstype))
 		goto out;