nir/passthrough_gs: flesh out gs_in_prim

geometry shaders don't specify the input topology, only the class of topology.
normalize when generating a passthrough gs.

asahi will be more picky about this in the future.

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Antonino Maniscalco <antonino.maniscalco@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27457>

src/compiler/nir/nir_passthrough_gs.c

@@ -34,7 +34,7 @@ gs_in_prim_for_topology(enum mesa_prim prim)
    case MESA_PRIM_QUADS:
       return MESA_PRIM_LINES_ADJACENCY;
    default:
-      return prim;
+      return u_decomposed_prim(prim);
    }
 }