drivers/net: eliminate irq handler impossible checks, needless casts

- Eliminate check for irq handler 'dev_id==NULL' where the
  condition never occurs.

- Eliminate needless casts to/from void*

Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/drivers/net/dgrs.c b/drivers/net/dgrs.c
index 6b1234b..a795202 100644
--- a/drivers/net/dgrs.c
+++ b/drivers/net/dgrs.c
@@ -897,8 +897,8 @@
 
 static irqreturn_t dgrs_intr(int irq, void *dev_id)
 {
-	struct net_device	*dev0 = (struct net_device *) dev_id;
-	DGRS_PRIV	*priv0 = (DGRS_PRIV *) dev0->priv;
+	struct net_device	*dev0 = dev_id;
+	DGRS_PRIV	*priv0 = dev0->priv;
 	I596_CB		*cbp;
 	int		cmd;
 	int		i;