PM / devfreq: fix initialization of current frequency in last status

PM / devfreq: fix initialization of current frequency in last status

Some systems need current frequency from last_status for calculation
but it is zeroed during initialization. When the device starts there is
no history, but we can assume that the last frequency was the
same as the initial frequency (which is also used in 'previous_freq').
The log shows the result of this misinterpreted value.
[    2.042847] ... Failed to get voltage for frequency 0: -34

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
Reviewed-by: Javi Merino <javi.merino@arm.com>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>