cpufreq: interactive: Fix freeing of cached tunabled during module_exit()

To avoid multiple frees of an allocated tunables struct during
module_exit(), the pointer to the allocated tunables should be stored in
only one of the per-CPU cached_tunables pointer.

So, in the case of per policy governor configuration, store the cached
values in the pointer of first CPU in a policy. In the case of one governor
across all policies, store it in the CPU0 pointer.

Change-Id: Id4334246491519ac91ab725a8758b2748f743bb0
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>