sconeserver: add patch to fix build issue

Fixes:

  http://autobuild.buildroot.org/results/f28/f2856c00d99fbf9ce882442ab7b868ccc4966388/build-end.log



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Simon Dawson <spdawson@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>