mesa: s/union gl_dlist_node/Node/ in dlist.c code
mesa: s/union gl_dlist_node/Node/ in dlist.c code

Just minor clean-up.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler