wvstreams: fix build failures

Add a patch to fix wvstreams build failures such as
http://autobuild.buildroot.org/results/8cb2904113a5e63d6170c085f77a8040d50a0138/build-end.log

.

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