libs: pixmap: Fix a pixmap creation crash.
libs: pixmap: Fix a pixmap creation crash.

We use GST_VAAPI_OBJECT_NATIVE_DISPLAY with wrong parameter for x11
pixmap creation, which causes crash if we run the internal test case
of:

test-decode --pixmap

ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi