drm/radeon/dpm: fix uninitialized read from stack in kv_dpm_late_enable

If we take the false branch of the if quoted in the diff below, we
end up doing a return ret, without ever having initialized it.

Picked up by coverity.

Signed-off-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>