clocksource, acpi_pm.c: fix check for monotonicity

Actually check the monotonicity of the ACPI PMTMR ten times, only delay for
0.9 miliseconds at most, and bail out early if some problem is determined.

Reported-by: Jochen Voß <jochen.voss@googlemail.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>