cpufreq / intel_pstate: Set timer timeout correctly

The current calculation of the delay time is wrong and a cut and
paste error from a previous experimental driver.  This can result in
the timeout being set to jiffies + 1 which setup the driver to race
with itself if the APIC timer interrupt happens at just the right
time.

References: https://bugzilla.redhat.com/show_bug.cgi?id=920289


Reported-by: Adam Williamson <awilliam@redhat.com>
Reported-and-tested-by: Parag Warudkar <parag.lkml@gmail.com>
Signed-off-by: Dirk Brandewie <dirk.j.brandewie@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>