RDMA/hns: Check return value of kzalloc

RDMA/hns: Check return value of kzalloc

When lp_qp_work is NULL, we should return ENOMEM.  In order to do so,
we had to make some upper layer functions return a value instead
of being void type so we can propagate the error up the stack.

This patch fixes the smatch error as below:
drivers/infiniband/hw/hns/hns_roce_hw_v1.c:918 hns_roce_v1_recreate_lp_qp()
error: potential null dereference 'lp_qp_work'.  (kzalloc returns null)

Signed-off-by: Wei Hu (Xavier) <xavier.huwei@huawei.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Shaobo Xu <xushaobo2@huawei.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>