xml: Cleanup libxml2 parser when exiting library
xml: Cleanup libxml2 parser when exiting library

When libiio is unloaded (when the client program exits), cleanup libxml2
so that memory analyzer tools like Valgrind won't detect a memory leak.

Signed-off-by: Paul Cercueil <a027184a55211cd23e3f3094f1fdc728df5e0500@crapouillou.net>

analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio,analogdevicesinc/libiio