igb: Use PCI Express Capability accessors

Use PCI Express Capability access functions to simplify igb driver.

[bhelgaas: split e1000e and igb into separate patches]
Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -6539,28 +6539,20 @@ static int igb_ioctl(struct net_device *netdev, struct ifreq *ifr, int cmd)
 s32 igb_read_pcie_cap_reg(struct e1000_hw *hw, u32 reg, u16 *value)
 {
 	struct igb_adapter *adapter = hw->back;
-	u16 cap_offset;
 
-	cap_offset = adapter->pdev->pcie_cap;
-	if (!cap_offset)
+	if (pcie_capability_read_word(adapter->pdev, reg, value))
 		return -E1000_ERR_CONFIG;
 
-	pci_read_config_word(adapter->pdev, cap_offset + reg, value);
-
 	return 0;
 }
 
 s32 igb_write_pcie_cap_reg(struct e1000_hw *hw, u32 reg, u16 *value)
 {
 	struct igb_adapter *adapter = hw->back;
-	u16 cap_offset;
 
-	cap_offset = adapter->pdev->pcie_cap;
-	if (!cap_offset)
+	if (pcie_capability_write_word(adapter->pdev, reg, *value))
 		return -E1000_ERR_CONFIG;
 
-	pci_write_config_word(adapter->pdev, cap_offset + reg, *value);
-
 	return 0;
 }