drm/nouveau/fan: handle the cases where we are outside of the linear zone

This fixes a bug where, when temperature is outside of the linear range, fan
pwm would be outside of the allowed range ([0, 100]) and could get negative in
some cases.

It seems like a regression that happened when we re-worked the fan management
logic before merging.
Tested-by: Ozan Çağlayan <ozancag@gmail.com>
Signed-off-by: Martin Peres <martin.peres@labri.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/subdev/therm/base.c

@@ -71,6 +71,13 @@ nouveau_therm_update_linear(struct nouveau_therm *therm)
 	u8  temp = therm->temp_get(therm);
 	u16 duty;
 
+	/* handle the non-linear part first */
+	if (temp < linear_min_temp)
+		return priv->fan->bios.min_duty;
+	else if (temp > linear_max_temp)
+		return priv->fan->bios.max_duty;
+
+	/* we are in the linear zone */
 	duty  = (temp - linear_min_temp);
 	duty *= (priv->fan->bios.max_duty - priv->fan->bios.min_duty);
 	duty /= (linear_max_temp - linear_min_temp);