PCI: Don't print anything while decoding is disabled

If we try to print to the console device while its decoding is disabled,
the system will hang.

Reported-and-tested-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Olof Johansson <olof@lixom.net>