package/nvidia-driver: fix build without X.org drivers

package/nvidia-driver: fix build without X.org drivers

Fix the following build failure without BR2_PACKAGE_NVIDIA_DRIVER_XORG
raised since commit 9cda982855315d683d4880e6bb2a129133ea7213:

ln: failed to create symbolic link '/tmp/instance-0/output-1/target/usr/lib/xorg/modules/extensions/libglx.so': No such file or directory

Fixes:
 - http://autobuild.buildroot.org/results/c2e7a826c105363309f70a3fcfe28bd53efcb94a

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Vincent Fazio <vfazio@xes-inc.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>