net: stmmac: Fix possible deadlock when disabling EEE support

When stmmac_eee_init() is called to disable EEE support, then the timer
for EEE support is stopped and we return from the function. Prior to
stopping the timer, a mutex was acquired but in this case it is never
released and so could cause a deadlock. Fix this by releasing the mutex
prior to returning from stmmax_eee_init() when stopping the EEE timer.

Fixes: 74371272f97f ("net: stmmac: Convert to phylink and remove phylib logic")
Signed-off-by: Jon Hunter <[e-mail]>
Tested-by: Thierry Reding <[e-mail]>
Acked-by: Willem de Bruijn <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

···
 		netdev_dbg(priv->dev, "disable EEE\n");
 		del_timer_sync(&priv->eee_ctrl_timer);
 		stmmac_set_eee_timer(priv, priv->hw, 0, tx_lpi_timer);
+		mutex_unlock(&priv->lock);
 		return false;
 	}