PCI: sysfs: Update ROM to include default owner write access

The PCI sysfs ROM interface requires an enabling write to access the ROM
image, but the default file mode is 0400.  The original proposed patch
adding sysfs ROM support was a true read-only interface, with the
enabling bit coming in as a feature request.  I suspect it was simply an
oversight that the file mode didn't get updated to match the API.

Acked-by: Chris Wright <chrisw@redhat.com>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>