PCI: Use FIELD_GET() in Sapphire RX 5600 XT Pulse quirk

Use FIELD_GET() to remove dependences on the field position, i.e., the
shift value.  No functional change intended.

Separate because this isn't as trivial as the other FIELD_GET() changes.

See 907830b0 ("PCI: Add a REBAR size quirk for Sapphire RX 5600 XT
Pulse")

Link: https://lore.kernel.org/r/20231010204436.1000644-3-helgaas@kernel.orgSigned-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@amd.com>

drivers/pci/pci.c

@@ -3750,14 +3750,14 @@ u32 pci_rebar_get_possible_sizes(struct pci_dev *pdev, int bar)
 		return 0;
 
 	pci_read_config_dword(pdev, pos + PCI_REBAR_CAP, &cap);
-	cap &= PCI_REBAR_CAP_SIZES;
+	cap = FIELD_GET(PCI_REBAR_CAP_SIZES, cap);
 
 	/* Sapphire RX 5600 XT Pulse has an invalid cap dword for BAR 0 */
 	if (pdev->vendor == PCI_VENDOR_ID_ATI && pdev->device == 0x731f &&
-	    bar == 0 && cap == 0x7000)
-		cap = 0x3f000;
+	    bar == 0 && cap == 0x700)
+		return 0x3f00;
 
-	return cap >> 4;
+	return cap;
 }
 EXPORT_SYMBOL(pci_rebar_get_possible_sizes);