goa: fix two compilation warnings

https://bugzilla.gnome.org/show_bug.cgi?id=591228
mount: fix compilation warning

https://bugzilla.gnome.org/show_bug.cgi?id=591228
smb: fix compilation warning

https://bugzilla.gnome.org/show_bug.cgi?id=591228
gdbus: fix compilation warning

https://bugzilla.gnome.org/show_bug.cgi?id=591228
cdda: fix two compilation warnings

https://bugzilla.gnome.org/show_bug.cgi?id=591228