net: ethernet: ax88796: avoid null pointer dereference

If platform_get_resource fails, mem2 is null.
Do not dereference null.
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/8390/ax88796.c

@@ -910,7 +910,8 @@ static int ax_probe(struct platform_device *pdev)
 	iounmap(ax->map2);
 
  exit_mem2:
-	release_mem_region(mem2->start, mem2_size);
+	if (mem2)
+		release_mem_region(mem2->start, mem2_size);
 
  exit_mem1:
 	iounmap(ei_local->mem);