IB/uverbs: Fix leak of XRC target QPs

The real QP is destroyed in case of the ref count reaches zero, but
for XRC target QPs this call was missed and caused to QP leaks.

Let's call to destroy for all flows.

Fixes: 0e0ec7e0

 ('RDMA/core: Export ib_open_qp() to share XRC...')
Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Signed-off-by: Noa Osherovich <noaos@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>