drivers: cpufreq: checks to avoid kernel crash in cpufreq_interactive

In cpufreq_governor_interactive, driver throws warning with WARN_ON
for !tunables and event != CPUFREQ_GOV_POLICY_INIT.
In case when tunables is NULL for event other than
CPUFREQ_GOV_POLICY_INIT, kernel will crash as there is no safe check
available before accessing tunables. So to handle such case and avoid
the kernel crash, return -EINVAL if WARN_ON returns TRUE.

Change-Id: I7a3a22d58e3c8a315a1cc1d31143649dc8807dee
Signed-off-by: gaurav jindal <gauravjindal1104@gmail.com>