xml: Simplify iio_populate_xml_context_helper
xml: Simplify iio_populate_xml_context_helper

Just return an error code and let the caller set errno itself.

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

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