linux-user: fix multi-threaded /proc/self/maps When reading our faked /proc/self/maps from a secondary thread, we get an invalid stack entry. This is because ts->stack_base is not initialized in non-primary threads. However, ts->info is, and the stack layout information we're looking for is there too. So let's use that one instead! Signed-off-by: Alexander Graf <agraf@suse.de> Signed-off-by: Riku Voipio <riku.voipio@linaro.org>