PCI: Don't print anything while decoding is disabled

If the console is a PCI device, and we try to print to it while its
decoding is disabled, the system will hang.  This particular printk hasn't
caused a problem yet, but it could, so this fixes it.

See also 0ff9514b

 ("PCI: Don't print anything while decoding is
disabled").

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>