cpufreq: scpi: Fix use after free

Free the priv structure only after we are done using it.

Fixes: 1690d8bb ("cpufreq: scpi/scmi: Fix freeing of dynamic OPPs")
Signed-off-by: Vincent Stehlé <vincent.stehle@laposte.net>
Cc: 4.20+ <stable@vger.kernel.org> # 4.20+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>