powerpc/fsl_uli1575: fix RTC quirk to work on MPC8572DS and MPC8610HPCD

powerpc/fsl_uli1575: fix RTC quirk to work on MPC8572DS and MPC8610HPCD

This patch fixes RTC on MPC8572DS boards: dummy read helps only when
reading at the end of the bridge's memory (i.e. outside of behind the
bridge devices' assigned regions).

With this change the quirk also makes RTC work on MPC8610HPCD, so it's
unlikely that this will break MPC8641HPCN or MPC8544DS boards.

Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>