st/mesa: use 'cso' instead of 'st->cso_context' in st_DrawTex()

Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Jose Fonseca <jfonseca@vmware.com>

src/mesa/state_tracker/st_cb_drawtex.c

@@ -256,7 +256,7 @@ st_DrawTex(struct gl_context *ctx, GLfloat x, GLfloat y, GLfloat z,
       velements[i].src_format = PIPE_FORMAT_R32G32B32A32_FLOAT;
    }
    cso_set_vertex_elements(cso, numAttribs, velements);
-   cso_set_stream_outputs(st->cso_context, 0, NULL, NULL);
+   cso_set_stream_outputs(cso, 0, NULL, NULL);
 
    /* viewport state: viewport matching window dims */
    {