atl2: remove unused variable 'atl2_driver_string'

drivers/net/ethernet/atheros/atlx/atl2.c:40:19: warning: ‘atl2_driver_string’ defined but not used [-Wunused-const-variable=]
 static const char atl2_driver_string[] = "Atheros(R) L2 Ethernet Driver";
                   ^~~~~~~~~~~~~~~~~~

commit ea973742 ("net/atheros: Clean atheros code from driver version")
left behind this, remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/atlx/atl2.c

@@ -37,7 +37,6 @@
 #include "atl2.h"
 
 static const char atl2_driver_name[] = "atl2";
-static const char atl2_driver_string[] = "Atheros(R) L2 Ethernet Driver";
 static const struct ethtool_ops atl2_ethtool_ops;
 
 MODULE_AUTHOR("Atheros Corporation <xiong.huang@atheros.com>, Chris Snook <csnook@redhat.com>");