linux-zigbee: fix build with gcc 7
Disable -Werror to avoid the fatal result of new gcc 7 format string warnings.
Fixes:
http://autobuild.buildroot.net/results/29c/29c72bc38042305310576be945c721b2fad95894/
http://autobuild.buildroot.net/results/a7d/a7d38d72834b94291eaff159da277b11e2f9d63a/
http://autobuild.buildroot.net/results/cfe/cfed5176075f0cb9e2f56ebef10f5d6c352baf10/
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit e1bebe18e54ad634bd6151445f009aa53038d765)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>