package/mesa3d: Fix dri config option

package/mesa3d: Fix dri config option

The option is constructed by AC_ARG_ENABLE and not AC_ARG_WITH:
http://cgit.freedesktop.org/mesa/mesa/tree/configure.ac?h=10.6#n726

Fixes
http://autobuild.buildroot.net/results/6e3/6e313e2a4b2ff092d187ac564f25c14aaaceb0dd/
http://autobuild.buildroot.net/results/e3c/e3c3e441038b72c78c8e94370baa036ab1effb6b/
http://autobuild.buildroot.net/results/11f/11f09260428a766d1f274843a9aebe220fd0e988/

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