uretprobes: Remove -ENOSYS as return probes implemented

Enclose return probes implementation.
Signed-off-by: Anton Arapov <anton@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>

kernel/events/uprobes.c

@@ -851,10 +851,6 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *
 	if (!uc->handler && !uc->ret_handler)
 		return -EINVAL;
 
-	/* TODO: Implement return probes */
-	if (uc->ret_handler)
-		return -ENOSYS;
-
 	/* Racy, just to catch the obvious mistakes */
 	if (offset > i_size_read(inode))
 		return -EINVAL;