lantiq: fix compilation warning in lantiq_etop_init

lantiq: fix compilation warning in lantiq_etop_init

Commit c5cc3d96109a ("lantiq: Change the data-type of mac address in ETOP driver")
changed the type of the mac variable. Since then, the priv->mac check always evaluates
as true, so this check can be removed.

This fix compilation warning:
drivers/net/ethernet/lantiq_etop.c: In function 'ltq_etop_init':
drivers/net/ethernet/lantiq_etop.c:775:13: warning: the comparison will always evaluate as 'true' for the address of 'mac' will never be NULL [-Waddress]
  775 |         if (priv->mac && !is_valid_ether_addr(mac.sa_data))
      |             ^~~~
drivers/net/ethernet/lantiq_etop.c:157:23: note: 'mac' declared here
  157 |         unsigned char mac[6];
      |
cc1: all warnings being treated as errors

Fixes: c5cc3d96109a ("lantiq: Change the data-type of mac address in ETOP driver")
Signed-off-by: Aleksander Jan Bajkowski <olek2@wp.pl>
[ fix wrong fixes tag format ]
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>