qvideosurfacegstsink: fixed calculation of supported formats.
qvideosurfacegstsink: fixed calculation of supported formats.

If the custom buffer pool is used, it's also necessary
to query the list of video surface formats with this handle type.

Change-Id: I8a38f4c75f37ed05fbfdcf0933023a6abef1b3e1
Reviewed-by: Mithra Pattison <860fddc7517327aaf7e8510c92a4748e54a8a05d@nokia.com>
Reviewed-by: Michael Goddard <3ec82c9d770214b86c58e0ffe200ac64c3ff8da3@nokia.com>
Reviewed-by: Jonas Rabbe <6e9178b26dba0cd114a9aed0874c56cbbaba6438@gmail.com>

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