net: hns3: Fixes initalization of RoCE handle and makes it conditional

When register a RoCE client with hnae3vf device, it needs to judge
the device whether support RoCE vf function. Otherwise, it will
lead to calltrace when RoCE is not support vf function and remove
roce device.

The calltrace as follows:
[   93.156614] Unable to handle kernel NULL pointer dereference at virtual address 00000015
 <SNIP>
[   93.278784] Call trace:
[   93.278788]  hnae3_match_n_instantiate+0x24/0xd8 [hnae3]
[   93.278790]  hnae3_register_client+0xcc/0x150 [hnae3]
[   93.278801]  hns_roce_hw_v2_init+0x18/0x1000 [hns_roce_hw_v2]
[   93.278805]  do_one_initcall+0x58/0x160
[   93.278807]  do_init_module+0x64/0x1d8
[   93.278809]  load_module+0x135c/0x15c8
[   93.278811]  SyS_finit_module+0x100/0x118
[   93.278816]  __sys_trace_return+0x0/0x4
[   93.278827] Code: aa0003f5 12001c56 aa1e03e0 d503201f (b9402660)

Fixes: e2cb1dec

 ("net: hns3: Add HNS3 VF HCL(Hardware Compatibility Layer) Support")
Reported-by: Xinwei Kong <kong.kongxinwei@hisilicon.com>
Reported-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Lijun Ou <oulijun@huawei.com>
Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>