Revert "Don't try to use bogus bridge data"

Revert "Don't try to use bogus bridge data"

This reverts commit 2bda5b733bb12854760750c08138db95e77aea0c.

It actually conflicts with 9ba94caf57e3a8c3e9c6f3f5f068f4a7a7b3ff9d
which came earlier, but I didn't catch it probably because I did a blind
rebase before pushing.

When reading bridge bus info, we may need to read out the current bridge
info if the PCI bridge private is uninitialized, so remove the check at
the top that would always short circuit the case where the priv was
still 0.

References:
https://bugs.launchpad.net/ubuntu/+source/libpciaccess/+bug/681207.

Reported-by: Bryce Harrington <bryce@canonical.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>