[ena] Fix spurious uninitialised variable warning on older versions of gcc

Some older versions of gcc (observed with gcc 4.7.2) report a spurious
uninitialised variable warning in ena_get_device_attributes().  Work
around this warning by manually inlining the relevant code (which has
only a single call site).

Reported-by: xbgmsharp <xbgmsharp@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/ena.c

@@ -540,54 +540,30 @@ static int ena_destroy_qp ( struct ena_nic *ena, struct ena_qp *qp ) {
 }
 
 /**
- * Get feature
+ * Get device attributes
  *
- * @v ena		ENA device
- * @v id		Feature identifier
- * @v feature		Feature to fill in
+ * @v netdev		Network device
  * @ret rc		Return status code
  */
-static int ena_get_feature ( struct ena_nic *ena, unsigned int id,
-			     union ena_feature **feature ) {
+static int ena_get_device_attributes ( struct net_device *netdev ) {
+	struct ena_nic *ena = netdev->priv;
 	union ena_aq_req *req;
 	union ena_acq_rsp *rsp;
+	union ena_feature *feature;
 	int rc;
 
 	/* Construct request */
 	req = ena_admin_req ( ena );
 	req->header.opcode = ENA_GET_FEATURE;
-	req->get_feature.id = id;
+	req->get_feature.id = ENA_DEVICE_ATTRIBUTES;
 
 	/* Issue request */
 	if ( ( rc = ena_admin ( ena, req, &rsp ) ) != 0 )
 		return rc;
 
 	/* Parse response */
-	*feature = &rsp->get_feature.feature;
-
-	return 0;
-}
-
-/**
- * Get device attributes
- *
- * @v netdev		Network device
- * @ret rc		Return status code
- */
-static int ena_get_device_attributes ( struct net_device *netdev ) {
-	struct ena_nic *ena = netdev->priv;
-	union ena_feature *feature;
-	int rc;
-
-	/* Get device attributes */
-	if ( ( rc = ena_get_feature ( ena, ENA_DEVICE_ATTRIBUTES,
-				      &feature ) ) != 0 )
-		return rc;
-
-	/* Extract MAC address */
+	feature = &rsp->get_feature.feature;
 	memcpy ( netdev->hw_addr, feature->device.mac, ETH_ALEN );
-
-	/* Extract MTU */
 	netdev->max_pkt_len = le32_to_cpu ( feature->device.mtu );
 
 	DBGC ( ena, "ENA %p MAC %s MTU %zd\n",