cxgb4: Remove some dead code

This 'BUG_ON(!ep)' can never trigger because we have:
   if (!ep)
      return 0;
just a few lines above. So it can be removed safely.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>