pci: align ioport special case for x86 in read/write/unmap

Commit b8eb345378bd ("pci: ignore devices already managed in Linux when
mapping x86 ioport") did not update other parts of the ioport api.

The application is not supposed to call these read/write/unmap ioport
functions if map call failed but I prefer aligning the code for the sake
of consistency.

Signed-off-by: David Marchand <david.marchand@6wind.com>