net: mvpp2: fix the mac address used when using PPv2.2

The mac address is only retrieved from h/w when using PPv2.1. Otherwise
the variable holding it is still checked and used if it contains a valid
value. As the variable isn't initialized to an invalid mac address
value, we end up with random mac addresses which can be the same for all
the ports handled by this PPv2 driver.

Fixes this by initializing the h/w mac address variable to {0}, which is
an invalid mac address value. This way the random assignation fallback
is called and all ports end up with their own addresses.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Fixes: 26975821 ("net: mvpp2: handle misc PPv2.1/PPv2.2 differences")
Signed-off-by: David S. Miller <davem@davemloft.net>