x86: mrst: Remove apb timer read workaround

APB timer current count was unreliable in the earlier silicon, which
could result in time going backwards. This problem has been fixed in
the current silicon stepping. This patch removes the workaround which
was used to check and prevent timer rolling back when APB timer is
used as clocksource device.

The workaround code was also flawed by potential race condition
around the cached read value last_read. Though a fix can be done
by assigning last_read to a local variable at the beginning of
apbt_read_clocksource(), but this is not necessary anymore.

[ tglx: A sane timer on an Intel chip - I can't believe it ]

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Alan Cox <alan@linux.intel.com>
LKML-Reference: <1298065374-25532-1-git-send-email-jacob.jun.pan@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>