RDMA/rxe: Fix the error caused by qp->sk

RDMA/rxe: Fix the error caused by qp->sk

When sock_create_kern in the function rxe_qp_init_req fails,
qp->sk is set to NULL.

Then the function rxe_create_qp will call rxe_qp_do_cleanup
to handle allocated resource.

Before handling qp->sk, this variable should be checked.

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20220822011615.805603-3-yanjun.zhu@linux.dev
Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Reviewed-by: Li Zhijian <lizhijian@fujitsu.com>
Reviewed-by: Bob Pearson <rpearsonhpe@gmail.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>