RDMA/srp: Fix NULL deref at srp_destroy_qp()

If srp_init_qp() fails at srp_create_ch_ib() then ch->send_cq
may be NULL.
Calling directly to ib_destroy_qp() is sufficient because
no work requests were posted on the created qp.

Fixes: 9294000d ("IB/srp: Drain the send queue before destroying a QP")
Cc: <stable@vger.kernel.org>
Signed-off-by: Israel Rukshin <israelr@mellanox.com>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Bart van Assche <bart.vanassche@sandisk.com&gt;-->
Signed-off-by: Doug Ledford <dledford@redhat.com>