suport/download: force svn to be non-interactive

Fixes:
    http://autobuild.buildroot.org/results/2af/2af7412846c576089f8596857ab8c81ac31c1bed/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: André Hentschel <nerv@dawncrow.de>
Reviewed-by: André Hentschel <nerv@dawncrow.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>