cpufreq: schedutil: Fix UAF issue

sugov_tunables are getting deleted with kobject release() in
'commit 67c98e02 ("cpufreq: schedutil: Use kobject release()
method to free sugov_tunables")'. So save tunables before freeing.

Change-Id: I9df2604210cb071bb907a39cf7fcc1131e4de5f8
Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>