ACPI: C-States: only demote on current bus mastering activity

Only if bus master activity is going on at the present, we should avoid
entering C3-type sleep, as it might be a faulty transition.  As long as the
bm_activity bitmask was based on the number of calls to the ACPI idle
function, looking at previous moments made sense.  Now, with it being based on
what happened this jiffy, looking at this jiffy should be sufficient.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>