owfs: install python bindings in the correct location

The owfs build system has a pretty complicated way of configuring the
Python bindings. It ends up with setting PYSITEDIR to the host-python
site-packages path, and it still prepends DESTDIR to that.

As a simple fix, override PYSITEDIR with the correct value on the make
command line.

Fixes:
http://autobuild.buildroot.net/results/200/200846650641494290aa67d28ea6fb2c9351d4dc
http://autobuild.buildroot.net/results/99c/99c00248dd8b00071bcdbc73336cc276c68a4c16


and many more

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>