PCI: Align PCIe capability and PCI accessor return values

The PCI config accessors (pci_read_config_word(), et al) return
PCIBIOS_SUCCESSFUL (zero) or positive error values like
PCIBIOS_FUNC_NOT_SUPPORTED.

The PCIe capability accessors similarly return PCIBIOS errors, but in
addition, they can return -EINVAL.  This makes it harder than it should be
to check for errors.

Return PCIBIOS_BAD_REGISTER_NUMBER instead of -EINVAL in all PCIe
capability accessors.

Suggested-by: Bjorn Helgaas <bjorn@helgaas.com>
Link: https://lore.kernel.org/r/20200615073225.24061-9-refactormyself@gmail.com
Signed-off-by: Bolarinwa Olayemi Saheed <refactormyself@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/access.c

@@ -409,7 +409,7 @@ int pcie_capability_read_word(struct pci_dev *dev, int pos, u16 *val)
 
 	*val = 0;
 	if (pos & 1)
-		return -EINVAL;
+		return PCIBIOS_BAD_REGISTER_NUMBER;
 
 	if (pcie_capability_reg_implemented(dev, pos)) {
 		ret = pci_read_config_word(dev, pci_pcie_cap(dev) + pos, val);
@@ -444,7 +444,7 @@ int pcie_capability_read_dword(struct pci_dev *dev, int pos, u32 *val)
 
 	*val = 0;
 	if (pos & 3)
-		return -EINVAL;
+		return PCIBIOS_BAD_REGISTER_NUMBER;
 
 	if (pcie_capability_reg_implemented(dev, pos)) {
 		ret = pci_read_config_dword(dev, pci_pcie_cap(dev) + pos, val);
@@ -469,7 +469,7 @@ EXPORT_SYMBOL(pcie_capability_read_dword);
 int pcie_capability_write_word(struct pci_dev *dev, int pos, u16 val)
 {
 	if (pos & 1)
-		return -EINVAL;
+		return PCIBIOS_BAD_REGISTER_NUMBER;
 
 	if (!pcie_capability_reg_implemented(dev, pos))
 		return 0;
@@ -481,7 +481,7 @@ EXPORT_SYMBOL(pcie_capability_write_word);
 int pcie_capability_write_dword(struct pci_dev *dev, int pos, u32 val)
 {
 	if (pos & 3)
-		return -EINVAL;
+		return PCIBIOS_BAD_REGISTER_NUMBER;
 
 	if (!pcie_capability_reg_implemented(dev, pos))
 		return 0;