new helper: file_inode(file)

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/relay.c b/kernel/relay.c
index e8cd202..01ab081 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -1139,7 +1139,7 @@
 	if (!desc->count)
 		return 0;
 
-	mutex_lock(&filp->f_path.dentry->d_inode->i_mutex);
+	mutex_lock(&file_inode(filp)->i_mutex);
 	do {
 		if (!relay_file_read_avail(buf, *ppos))
 			break;
@@ -1159,7 +1159,7 @@
 			*ppos = relay_file_read_end_pos(buf, read_start, ret);
 		}
 	} while (desc->count && ret);
-	mutex_unlock(&filp->f_path.dentry->d_inode->i_mutex);
+	mutex_unlock(&file_inode(filp)->i_mutex);
 
 	return desc->written;
 }