RDMA/ocrdma: Fix error return code in ocrdma_set_create_qp_rq_cmd()

Fix to return -ENOMEM in the alloc dma coherent error case instead of
0, as done elsewhere in this function.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Roland Dreier <roland@purestorage.com>