do_epoll_ctl(): clean the failure exits up a bit

commit 52c479697c9b73f628140dcdfcd39ea302d05482 upstream.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit b3ce6ca9)