drivers/net: Move a dereference below a NULL test

If the NULL test is necessary, then the dereferences should be moved below
the NULL test.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
type T;
expression E,E1;
identifier i,fld;
statement S;
@@

- T i = E->fld;
+ T i;
  ... when != E=E1
      when != i
  BUG_ON (E == NULL||...);
+ i = E->fld;
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ibm_newemac/rgmii.c

@@ -188,11 +188,12 @@ void rgmii_put_mdio(struct of_device *ofdev, int input)
 void rgmii_detach(struct of_device *ofdev, int input)
 {
 	struct rgmii_instance *dev = dev_get_drvdata(&ofdev->dev);
-	struct rgmii_regs __iomem *p = dev->base;
-
-	mutex_lock(&dev->lock);
+	struct rgmii_regs __iomem *p;
 
 	BUG_ON(!dev || dev->users == 0);
+	p = dev->base;
+
+	mutex_lock(&dev->lock);
 
 	RGMII_DBG(dev, "detach(%d)" NL, input);