igb: fix legacy mode irq issue

I booted an igb kernel with the option pci=nomsi and instantly noticed
that interrupts no longer worked on my igb device.  I took a look at the
interrupt initialization and quickly discovered a comment stating:

"DO NOT USE EIAME or IAME in legacy mode"

It seemed a bit odd that bits to enable IAM were being set in legacy
interrupt mode, so I dropped out the following parts and interrupts
began working fine again.

[Updated code flow and a nitpick spelling error --Auke]
Signed-off-by: Andy Gospodarek <andy@greyhouse.net>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/net/igb/igb_main.c

@@ -439,7 +439,7 @@ static int igb_request_irq(struct igb_adapter *adapter)
 		err = igb_request_msix(adapter);
 		if (!err) {
 			/* enable IAM, auto-mask,
-			 * DO NOT USE EIAME or IAME in legacy mode */
+			 * DO NOT USE EIAM or IAM in legacy mode */
 			wr32(E1000_IAM, IMS_ENABLE_MASK);
 			goto request_done;
 		}
@@ -465,14 +465,9 @@ static int igb_request_irq(struct igb_adapter *adapter)
 	err = request_irq(adapter->pdev->irq, &igb_intr, IRQF_SHARED,
 			  netdev->name, netdev);
 
-	if (err) {
+	if (err)
 		dev_err(&adapter->pdev->dev, "Error %d getting interrupt\n",
 			err);
-		goto request_done;
-	}
-
-	/* enable IAM, auto-mask */
-	wr32(E1000_IAM, IMS_ENABLE_MASK);
 
 request_done:
 	return err;