gbm/dri: cleanup memory leak on teardown
gbm/dri: cleanup memory leak on teardown

During teardown we free the driver_configs list pointer, but we forget
to deallocate each config in that list.

Signed-off-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>
Reviewed-and-tested-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler