PCI: Update pci_find_capability() stub return types

PCI: Update pci_find_capability() stub return types

f646c2a0a668 ("PCI: Return u8 from pci_find_capability() and similar") and
ee8b1c478a9f ("PCI: Return u16 from pci_find_ext_capability() and similar")
updated the return type of the extern declarations, but neglected to update
the type of the stubs used when CONFIG_PCI is not enabled.

Update them to match the extern declarations.

Link: https://lore.kernel.org/r/20240327180234.1529164-1-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>