selftests: mptcp: fix error path

commit 4a2f48992ddf4b8c2fba846c6754089edae6db5a upstream.

pm_nl_check_endpoint() currently calls an not existing helper
to mark the test as failed. Fix the wrong call.

Fixes: 03668c65

 ("selftests: mptcp: join: rework detailed report")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ Conflicts in mptcp_join.sh because the context has changed in commit
  571d7966

 ("selftests: mptcp: join: update endpoint ops") which is
  not in this version. This commit is unrelated to this modification. ]
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>