svga: change error handling convention for svga_set_stream_output()

In general, the functions which emit commands to the command buffer check
for failure and return a PIPE_ERROR_x code.  It's up to the caller to
flush the buffer and retry the command.

But svga_set_stream_output() did its own flushing and the callers never
checked the return value (though, it would always be PIPE_OK) in practice.

This patch changes svga_set_stream_output() so that it does not call
svga_context_flush() when the buffer is full.  And we update the callers
to check the return value as we do for other functions, like
svga_set_shader().

No Piglit regressions.  Also tested w/ Nature demo.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>

src/gallium/drivers/svga/svga_pipe_streamout.c

 svga_set_stream_output(struct svga_context *svga,
                        struct svga_stream_output *streamout)
 {
-   enum pipe_error ret = PIPE_OK;
    unsigned id = streamout ? streamout->id : SVGA3D_INVALID_ID;
 
    if (!svga_have_vgpu10(svga)) {
             streamout, id);
 
    if (svga->current_so != streamout) {
-      /* Save current SO state */
-      svga->current_so = streamout;
-
-      ret = SVGA3D_vgpu10_SetStreamOutput(svga->swc, id);
+      enum pipe_error ret = SVGA3D_vgpu10_SetStreamOutput(svga->swc, id);
       if (ret != PIPE_OK) {
-         svga_context_flush(svga, NULL);
-         ret = SVGA3D_vgpu10_SetStreamOutput(svga->swc, id);
+         return ret;
       }
+
+      svga->current_so = streamout;
    }
 
-   return ret;
+   return PIPE_OK;
 }
 
 void

src/gallium/drivers/svga/svga_state_gs.c

     * it instead of the one from the vertex shader.
     */
    if (svga_have_gs_streamout(svga)) {
-      svga_set_stream_output(svga, gs->base.stream_output);
+      ret = svga_set_stream_output(svga, gs->base.stream_output);
+      if (ret != PIPE_OK) {
+         goto done;
+      }
    }
    else if (!svga_have_vs_streamout(svga)) {
       /* turn off stream out */
-      svga_set_stream_output(svga, NULL);
+      ret = svga_set_stream_output(svga, NULL);
+      if (ret != PIPE_OK) {
+         goto done;
+      }
    }
 
    /* SVGA_NEW_NEED_SWTNL */

src/gallium/drivers/svga/svga_state_vs.c

       /* No GS stream out */
       if (svga_have_vs_streamout(svga)) {
          /* Set VS stream out */
-         svga_set_stream_output(svga, vs->base.stream_output);
+         ret = svga_set_stream_output(svga, vs->base.stream_output);
       }
       else {
          /* turn off stream out */
-         svga_set_stream_output(svga, NULL);
+         ret = svga_set_stream_output(svga, NULL);
+      }
+      if (ret != PIPE_OK) {
+         goto done;
       }
    }