igb: Use FIELD_GET() to extract Link Width

Use FIELD_GET() to extract PCIe Negotiated Link Width field instead of
custom masking and shifting.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Pucha Himasekhar Reddy <himasekharx.reddy.pucha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igb/e1000_mac.c

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright(c) 2007 - 2018 Intel Corporation. */
 
+#include <linux/bitfield.h>
 #include <linux/if_ether.h>
 #include <linux/delay.h>
 #include <linux/pci.h>
@@ -50,9 +51,8 @@ s32 igb_get_bus_info_pcie(struct e1000_hw *hw)
 			break;
 		}
 
-		bus->width = (enum e1000_bus_width)((pcie_link_status &
-						     PCI_EXP_LNKSTA_NLW) >>
-						     PCI_EXP_LNKSTA_NLW_SHIFT);
+		bus->width = (enum e1000_bus_width)FIELD_GET(PCI_EXP_LNKSTA_NLW,
+							     pcie_link_status);
 	}
 
 	reg = rd32(E1000_STATUS);