i965/gen6/gs: Assign geometry shader VUE map properly.

i965/gen6/gs: Assign geometry shader VUE map properly.

So far in gen6 we only used geometry shaders to implement transform feedback
in vertex shaders, so we assumed that the VUE map for the geometry shader
stage was always the same as for the vertex shader stage. This is no longer
true now that we support user provided geometry shaders in gen6 too.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>