package/x11r7/xdriver_xf86-video-siliconmotion: Fix compile warnings being treated...

package/x11r7/xdriver_xf86-video-siliconmotion: Fix compile warnings being treated as error

Fixes
http://autobuild.buildroot.net/results/059/059d771cb39532dee73a5f50e24b3441005ed38b/
http://autobuild.buildroot.net/results/542/5429dd3f07430cf1487a8cfa82ba55e66a640473/
http://autobuild.buildroot.net/results/073/073105a692033665d31b2dc034eff2e0fdca7f10/
http://autobuild.buildroot.net/results/018/01805d60b8b046122d357e2559268e8a45dcf9d3/
and many others

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>