gstreamer1.0-python: Set internal python library path correcty

The library hardcodes paths to the python library internally and currently
these are build paths. Fix this to use the correct target path and
fix reproducibility in the process.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit 4c190e8c)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>