mpd: fix upnp build failure

Add patch to fix build failure:
http://autobuild.buildroot.net/results/7ff/7ff28551b9c72658eb75394e7cbd1904861f23e3/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>