drm/amd/powerplay: don't give up if DPM is already running

Currently the driver crashes if smu7_enable_dpm_tasks() returns early,
which it does if DPM is already active. It seems to be better just to
continue anyway, at least I haven't noticed any ill effects. It's also
unclear at what state the hardware was left by the previous driver, so
IMO it's better to always fully initialize.

Way to reproduce:
with GPU passthrough.
forced power off the VM or forced reset the VM
without shutting down the Os.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Reviewed-by: Edward O'Callaghan <funfunctor@folklore1984.net>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>