kill file_permission() completely

convert the last remaining caller to inode_permission()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

kernel/cgroup.c

@@ -3542,7 +3542,8 @@ static int cgroup_write_event_control(struct cgroup *cgrp, struct cftype *cft,
 	}
 
 	/* the process need read permission on control file */
-	ret = file_permission(cfile, MAY_READ);
+	/* AV: shouldn't we check that it's been opened for read instead? */
+	ret = inode_permission(cfile->f_path.dentry->d_inode, MAY_READ);
 	if (ret < 0)
 		goto fail;