b53: Fix build warning.

   drivers/net/dsa/b53/b53_srab.c: In function 'b53_srab_probe':
>> drivers/net/dsa/b53/b53_srab.c:388:20: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
      pdata->chip_id = (u32)of_id->data;
                       ^
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/dsa/b53/b53_srab.c

@@ -393,7 +393,7 @@ static int b53_srab_probe(struct platform_device *pdev)
 		if (!pdata)
 			return -ENOMEM;
 
-		pdata->chip_id = (u32)of_id->data;
+		pdata->chip_id = (u32)(unsigned long)of_id->data;
 	}
 
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);