soc: marvell: remove useless condition judgment

commit 92a4f56a(driver: soc: marvell: phy7121p MACsec) introduced
"add VLAN port case". It seems to compare a char array with 0 in function
phy_debug_mac_sec_write(), it is useless and introduces below warning, we
can remove it temporarily and restore it if necessary in the future.

drivers/soc/marvell/phy_7121p_macadv_features.c: In function 'phy_debug_mac_sec_write':
drivers/soc/marvell/phy_7121p_macadv_features.c:900:57: warning: the comparison will always evaluate as 'false' for the     address of 'vlan_tag' will never be NULL [-Waddress]
  900 |                 if (mac_adv->data.vport_params.vlan_tag == 0)
      |                                                         ^~
drivers/soc/marvell/phy_7121p_macadv_features.c:287:23: note: 'vlan_tag' declared here
  287 |         unsigned char vlan_tag[4];
      |                       ^~~~~~~~

Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>