package/libbsd: disable for nds32

There is no support for nds32 in libbsd.

Fixes:
  http://autobuild.buildroot.net/results/eb79fbd8283f62ca08b85d851e3c817e0354f85c/



Signed-off-by: Nylon Chen <nylon7@andestech.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>