trace: Trace the correct version of the resource when setting the index buffer.

The trace driver was tracing the unwrapped version of the index buffer
when setting the index buffer.  This caused an assert validating that
a resource belonged to the trace driver to fail.  Instead, we'll log
the unmodified index buffer structure when setting the index buffer.

Signed-off-by: José Fonseca <jfonseca@vmware.com>

src/gallium/drivers/trace/tr_context.c

@@ -1002,7 +1002,7 @@ trace_context_set_index_buffer(struct pipe_context *_pipe,
    trace_dump_call_begin("pipe_context", "set_index_buffer");
 
    trace_dump_arg(ptr, pipe);
-   trace_dump_arg(index_buffer, ib);
+   trace_dump_arg(index_buffer, _ib);
 
    pipe->set_index_buffer(pipe, ib);