IB/mad: Fix null pointer dereference in local_completions()

handle_outgoing_dr_smp() can queue a struct ib_mad_local_private
*local on the mad_agent_priv->local_work work queue with
local->mad_priv == NULL if device->process_mad() returns
IB_MAD_RESULT_SUCCESS | IB_MAD_RESULT_REPLY and
(!ib_response_mad(&mad_priv->mad.mad) ||
!mad_agent_priv->agent.recv_handler).

In this case, local_completions() will be called with local->mad_priv
== NULL. The code does check for this case and skips calling
recv_mad_agent->agent.recv_handler() but recv == 0 so
kmem_cache_free() is called with a NULL pointer.

Also, since recv isn't reinitialized each time through the loop, it
can cause a memory leak if recv should have been zero.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>