drm/amd/powerplay: Fix psm_set_user_performance_state()

We now pass a pointer to a pointer which seems to be
what they meant in the first place.  The previous version
was modifying a pointer passed by value.

Fixes bug that was introduced by

commit 332798d40c2e91:drm/amd/powerplay: delete eventmgr layer in poweprlay

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-By: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>