net: stmmac: dwmac-qcom-ethqos: fix a regression on EMAC < 3

We must not assign plat_dat->dwmac4_addrs unconditionally as for
structures which don't set them, this will result in the core driver
using zeroes everywhere and breaking the driver for older HW. On EMAC < 2
the address should remain NULL.

Fixes: b6837619

 ("net: stmmac: dwmac-qcom-ethqos: Add EMAC3 support")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>