drm/nouveau/pm: do not stop reclocking if failing to set the fan speed

With the introduction of fan management modes, fan may not be drivable.
We should allow reclocking nonetheless.

This return was stupid to begin with since it may have left the card
in an intermediate state (clocks corresponding to a perflvl and voltage
corresponding to another one). The reclocking code will need to be
rewritten in a near-future in order to provide a better error handling.

Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Martin Peres <martin.peres@labri.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>