cpufreq: tegra186: Fix initial frequency

Commit 6cc3d0e9

 ("cpufreq: tegra186: add
CPUFREQ_NEED_INITIAL_FREQ_CHECK flag") fixed CPUFREQ support for
Tegra186 but as a consequence the following warnings are now seen on
boot ...

 cpufreq: cpufreq_online: CPU0: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU0: Unlisted initial frequency changed to: 2035200 KHz
 cpufreq: cpufreq_online: CPU1: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU1: Unlisted initial frequency changed to: 2035200 KHz
 cpufreq: cpufreq_online: CPU2: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU2: Unlisted initial frequency changed to: 2035200 KHz
 cpufreq: cpufreq_online: CPU3: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU3: Unlisted initial frequency changed to: 2035200 KHz
 cpufreq: cpufreq_online: CPU4: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU4: Unlisted initial frequency changed to: 2035200 KHz
 cpufreq: cpufreq_online: CPU5: Running at unlisted freq: 0 KHz
 cpufreq: cpufreq_online: CPU5: Unlisted initial frequency changed to: 2035200 KHz

Fix this by adding a 'get' callback for the Tegra186 CPUFREQ driver to
retrieve the current operating frequency for a given CPU. The 'get'
callback uses the current 'ndiv' value that is programmed to determine
that current operating frequency.

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
[ Viresh: Return 0 on error ]
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>