cpufreq/amd-pstate: Drop ret variable from amd_pstate_set_energy_pref_index()

The ret variable is not necessary.

Reviewed-and-tested-by: Dhananjay Ugwekar <dhananjay.ugwekar@amd.com>
Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Link: https://lore.kernel.org/r/20241209185248.16301-14-mario.limonciello@amd.com


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