RDMA/nes: Avoid memory allocation during CQ destroy

The memory allocation call can fail and cause to early return
from nes_desotroy_cq() function. This situation will cause to
memory leak of struct nes_cq. Rewrite function to avoid memory
allocation.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>