st/mesa: Don't record garbage streamout information in the non-SSO case.
breaks dEQP-GLES31.functional.tessellation.invariance.* on r600. All the tests pass without this patch, but with the patch applied
glGetQueryObjectuiv(queryObject, GL_QUERY_RESULT, &result);
returns zero in result for all the tests from this set, which is not correct.
A bit of digging showed that in these tests the driver only seems to write streamout data from the TES shader, but it somehow gets lost. My guess is that the driver at one point ignores the TF information attached at stages that are not the vertex shader, because before this patch the TES TF output information gets attached in each stage, and hence, also in the VS stage.