pci: intel: Fix error when enumerating multi-function PCIe device

Hardware return completion status non-zero when read from non exist
function in multi-function PCIe device. Return error will cause PCIe
enumeration fail.

Change it to return 0 and return value 0xffffffff when error.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
diff --git a/drivers/pci/pcie_intel_fpga.c b/drivers/pci/pcie_intel_fpga.c
index e74b35a..a096d1c 100644
--- a/drivers/pci/pcie_intel_fpga.c
+++ b/drivers/pci/pcie_intel_fpga.c
@@ -161,8 +161,10 @@
 			dw[count++] = cra_readl(pcie, RP_RXCPL_REG);
 			if (ctrl & RP_RXCPL_EOP) {
 				comp_status = TLP_COMP_STATUS(dw[1]);
-				if (comp_status)
-					return -EFAULT;
+				if (comp_status) {
+					*value = pci_get_ff(PCI_SIZE_32);
+					return 0;
+				}
 
 				if (value &&
 				    TLP_BYTE_COUNT(dw[1]) == sizeof(u32) &&