inter: Unref bus after usage

gst_pipeline_get_bus() returns a reference to a bus that needs to
be unreferenced after usage.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=734525
glbufferpool: Unref allocator after usage

gst_allocator_find() returns a reference to a GstAllocator.
This needs to be unreffed when the bufferpool is finalized.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=734523