RDMA/rxe: Fix BUG: KASAN: null-ptr-deref in rxe_qp_do_cleanup

In the Linux kernel, the following vulnerability has been resolved:

RDMA/rxe: Fix BUG: KASAN: null-ptr-deref in rxe_qp_do_cleanup

The function rxe_create_qp calls rxe_qp_from_init. If some error
occurs, the error handler of function rxe_qp_from_init will set
both scq and rcq to NULL.

Then rxe_create_qp calls rxe_put to handle qp. In the end,
rxe_qp_do_cleanup is called by rxe_put. rxe_qp_do_cleanup directly
accesses scq and rcq before checking them. This will cause
null-ptr-deref error.

The call graph is as below:

rxe_create_qp {
...
rxe_qp_from_init {
...
err1:
...
qp->rcq = NULL; <---rcq is set to NULL
qp->scq = NULL; <---scq is set to NULL
...
}

qp_init:
rxe_put{
...
rxe_qp_do_cleanup {
...
atomic_dec(&qp->scq->num_wq); <--- scq is accessed
...
atomic_dec(&qp->rcq->num_wq); <--- rcq is accessed
}
}