dpaa2-eth: Initialize mutex used in one step timestamping path

1588 Single Step Timestamping code path uses a mutex to
enforce atomicity for two events:
- update of ptp single step register
- transmit ptp event packet

Before this patch the mutex was not initialized. This
caused unexpected crashes in the Tx function.

Fixes: c5521189 ("dpaa2-eth: support PTP Sync packet one-step timestamping")
Signed-off-by: Radu Bulie <radu-andrei.bulie@nxp.com>
Reviewed-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/freescale/dpaa2/dpaa2-eth.c

@@ -4338,7 +4338,7 @@ static int dpaa2_eth_probe(struct fsl_mc_device *dpni_dev)
 	}
 
 	INIT_WORK(&priv->tx_onestep_tstamp, dpaa2_eth_tx_onestep_tstamp);
-
+	mutex_init(&priv->onestep_tstamp_lock);
 	skb_queue_head_init(&priv->tx_skbs);
 
 	priv->rx_copybreak = DPAA2_ETH_DEFAULT_COPYBREAK;