net: stmmac: fix possible memory leak in stmmac_dvr_probe()

The bitmap_free() should be called to free priv->af_xdp_zc_qps
when create_singlethread_workqueue() fails, otherwise there will
be a memory leak, so we add the err path error_wq_init to fix it.

Fixes: bba2556e

 ("net: stmmac: Enable RX via AF_XDP zero-copy")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>