omxbufferpool: Improve source code
omxbufferpool: Improve source code

Fix all warning messages on building

refs #90970
Signed-off-by: Thao Luong <ef4308e16b91b9bcf00aabc74dbe961cf8111f94@rvc.renesas.com>

renesas-rcar/gst-omx,renesas-rcar/gst-omx,renesas-rcar/gst-omx