Fix a few memory leaks.
Fix a few memory leaks.

XV Buffer pool was leaking, the sink delegate was leaking, and the
sink wasn't chaining to parent class so GstObject stuff was leaking.

Change-Id: I5d6b6fe59dfb2b3c5367dfde8331e5943167b55d
Reviewed-by: Dmytro Poplavskiy <72e04cfb587e72184d425a79cb5cea0021f0b982@nokia.com>

sergiusens/qtmultimedia,webOS-ports/qtmultimedia,jfaust/qtmultimedia,sergiusens/qtmultimedia,webOS-ports/qtmultimedia,webOS-ports/qtmultimedia,mer-qt/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,sergiusens/qtmultimedia,nezticle/qtmultimedia,sergiusens/qtmultimedia,jfaust/qtmultimedia,mer-qt/qtmultimedia,webOS-ports/qtmultimedia,nezticle/qtmultimedia,sergiusens/qtmultimedia,nezticle/qtmultimedia,nezticle/qtmultimedia,webOS-ports/qtmultimedia,mer-qt/qtmultimedia,nezticle/qtmultimedia,jfaust/qtmultimedia