RDMA/rxe: Fix "kernel NULL pointer dereference" error

RDMA/rxe: Fix "kernel NULL pointer dereference" error

When rxe_queue_init in the function rxe_qp_init_req fails,
both qp->req.task.func and qp->req.task.arg are not initialized.

Because of creation of qp fails, the function rxe_create_qp will
call rxe_qp_do_cleanup to handle allocated resource.

Before calling __rxe_do_task, both qp->req.task.func and
qp->req.task.arg should be checked.

Fixes: c4397c211d7d ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20220822011615.805603-2-yanjun.zhu@linux.dev
Reported-by: syzbot+ab99dc4c6e961eed8b8e@syzkaller.appspotmail.com
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>