ANDROID: dummy_cpufreq: Implement get()

Fixes panic in time_cpufreq_notifier+0x94 caused by notifying the x86
TSC synchronization code that a CPU frequency change has occurred, but
not properly updating policy->cur beforehand, causing a division by
zero.

Link: https://github.com/ClangBuiltLinux/linux/issues/756


Change-Id: I687093bbdb402a13341762bf9d91dd7f9daffe8b
Signed-off-by: Alistair Delva <adelva@google.com>