mesa: invalidate pipeline status after glUseProgramStages

This will cause validation to run during next draw, this is done
because possible changes in used stages and programs can cause
invalid pipeline state.

This fixes a subtest in following CTS test:
	ES31-CTS.sepshaderobjs.StateInteraction

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>

src/mesa/main/pipelineobj.c

@@ -341,6 +341,8 @@ _mesa_UseProgramStages(GLuint pipeline, GLbitfield stages, GLuint program)
 
    if ((stages & GL_COMPUTE_SHADER_BIT) != 0)
       _mesa_use_shader_program(ctx, GL_COMPUTE_SHADER, shProg, pipe);
+
+   pipe->Validated = false;
 }
 
 /**