[CPUFREQ][6/8] acpi-cpufreq: Eliminate get of current freq on notification

Only change the frequency if the state previously set is different
from what we are trying to set. We don't really have to get the current
frequency at this point.

Signed-off-by: Denis Sadykov <denis.m.sadykov@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Alexey Starikovskiy <alexey.y.starikovskiy@intel.com>
Signed-off-by: Dave Jones <davej@redhat.com>