PM / devfreq: governor_cpufreq: Output device name in debug print

Governor_cpufreq can scale multiple devfreq devices together. Output
devfreq device name in debug print to distinguish requests made
for each device.

Change-Id: I2f6856b66aae87dcb28830e318d20779233308de
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>