drm: nouveau: Fix build warning seen if HWMON is undefined

Fix:

nouveau_pm.c: In function ‘nouveau_hwmon_init’:
nouveau_pm.c:703:24: warning: unused variable ‘therm’ [-Wunused-variable]

Introduced by commit 095f979a (drm/nouveau/pm: fix build with HWMON off) which
fixed a build error but introduced a build warning.

Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_pm.c

@@ -698,10 +698,10 @@ static int
 nouveau_hwmon_init(struct drm_device *dev)
 {
 	struct nouveau_pm *pm = nouveau_pm(dev);
-	struct nouveau_drm *drm = nouveau_drm(dev);
-	struct nouveau_therm *therm = nouveau_therm(drm->device);
 
 #if defined(CONFIG_HWMON) || (defined(MODULE) && defined(CONFIG_HWMON_MODULE))
+	struct nouveau_drm *drm = nouveau_drm(dev);
+	struct nouveau_therm *therm = nouveau_therm(drm->device);
 	struct device *hwmon_dev;
 	int ret = 0;