drm/nouveau: have nv_mask return original register value

Signed-off-by: NBen Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -1255,12 +1255,11 @@ static inline void nv_wr32(struct drm_device *dev, unsigned reg, u32 val)
 	iowrite32_native(val, dev_priv->mmio + reg);
 }
 
-static inline void nv_mask(struct drm_device *dev, u32 reg, u32 mask, u32 val)
+static inline u32 nv_mask(struct drm_device *dev, u32 reg, u32 mask, u32 val)
 {
 	u32 tmp = nv_rd32(dev, reg);
-	tmp &= ~mask;
-	tmp |= val;
-	nv_wr32(dev, reg, tmp);
+	nv_wr32(dev, reg, (tmp & ~mask) | val);
+	return tmp;
 }
 
 static inline u8 nv_rd08(struct drm_device *dev, unsigned reg)