nir: add matrix_layout to nir_variable data

This will be used by the following patch.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4623>

src/compiler/glsl/glsl_to_nir.cpp

@@ -464,6 +464,7 @@ nir_visitor::visit(ir_variable *ir)
 
    var->data.precision = ir->data.precision;
    var->data.explicit_location = ir->data.explicit_location;
+   var->data.matrix_layout = ir->data.matrix_layout;
    var->data.from_named_ifc_block = ir->data.from_named_ifc_block;
    var->data.compact = false;