msm: cpufreq: Fix msm_cpufreq_get_freq() for sync CPUs

When CPUs are in sync, only CPU0 has a non-NULL cpu_clk. clk_get_rate()
on other cpu_clk will return 0. msm_cpufreq_get_freq() is used in multiple
places in cpufreq framework to determine current hardware frequency.

Fix msm_cpufreq_get_freq() to return the right hardware frequency for
systems with synchronous CPUs.

Change-Id: I6a880764ad51fa9a257a328798b38d574750686a
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>