cpufreq/amd-pstate: Drop cached epp_policy variable

epp_policy is not used by any of the current code and there
is no need to cache it.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20241209185248.16301-6-mario.limonciello@amd.com


Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>