scsi: fnic: Remove set but not used 'old_vlan'

This addresses the following gcc warning with "make W=1":

drivers/scsi/fnic/fnic_main.c: In function ‘fnic_set_vlan’:
drivers/scsi/fnic/fnic_main.c:555:6: warning: variable ‘old_vlan’ set
but not used [-Wunused-but-set-variable]
  555 |  u16 old_vlan;
      |      ^~~~~~~~

Link: https://lore.kernel.org/r/20200831081126.3251288-2-yanaijie@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/fnic/fnic_main.c

@@ -552,8 +552,7 @@ static u8 *fnic_get_mac(struct fc_lport *lport)
 
 static void fnic_set_vlan(struct fnic *fnic, u16 vlan_id)
 {
-	u16 old_vlan;
-	old_vlan = vnic_dev_set_default_vlan(fnic->vdev, vlan_id);
+	vnic_dev_set_default_vlan(fnic->vdev, vlan_id);
 }
 
 static int fnic_probe(struct pci_dev *pdev, const struct pci_device_id *ent)