drm/amd/powerplay: Fix double unlock bug in smu_sys_set_pp_table()

We already unlocked a few lines earlier so this code unlocks twice on
the success path.

Fixes: 289921b0

 ("drm/amd/powerplay: implement sysfs of pp_table for smu11 (v2)")
Reviewed-by: Huang Rui <ray.huang@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>