Hi,

when building fwupd binary-arch packages only (aka dpkg-buildpackage
-B), fwupd fails to build from source:

   * when building binary-arch only, the doc files are present in
     debian/tmp/usr/share/doc, so 'dh_install -pfwupd-doc usr/share/doc'
     is run.

   * 'dh_install -pfwupd-doc [...]' isn't doing anything, because
     fwupd-doc is arch:all and thus not considere in this run.

   * later on, the execution of 'dh_missing -a --fail-missing' makes
     the build fail.

There are multiple ways how to fix this and I don't know which one you
would prefer, so I didn't prepare a patch. Let me know if you want me to.

Regards,
Daniel