cpufreq: amd-pstate: fix memory leak on CPU EPP exit

The cpudata memory from kzalloc() in amd_pstate_epp_cpu_init() is
not freed in the analogous exit function, so fix that.

Signed-off-by: Peng Ma <andypma@tencent.com>
Acked-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Perry Yuan <Perry.Yuan@amd.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>