xgene: Fix build warning with ACPI disabled.

drivers/net/ethernet/apm/xgene/xgene_enet_hw.c: In function 'xgene_enet_phy_connect':
drivers/net/ethernet/apm/xgene/xgene_enet_hw.c:759:22: warning: unused variable 'adev' [-Wunused-variable]

Fixes: 8089a96f

 ("drivers: net: xgene: Add backward compatibility")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>