drm/fsl-dcu: do not update when modifying irq registers

The IRQ status and mask registers are not "double buffered" according
to the reference manual. Hence, there is no extra transfer/update
write needed when modifying these registers.
Signed-off-by: NStefan Agner <stefan@agner.ch>

drivers/gpu/drm/fsl-dcu/fsl_dcu_drm_drv.c

@@ -59,8 +59,6 @@ static int fsl_dcu_drm_irq_init(struct drm_device *dev)
 
 	regmap_write(fsl_dev->regmap, DCU_INT_STATUS, 0);
 	regmap_write(fsl_dev->regmap, DCU_INT_MASK, ~0);
-	regmap_write(fsl_dev->regmap, DCU_UPDATE_MODE,
-		     DCU_UPDATE_MODE_READREG);
 
 	return ret;
 }
@@ -139,8 +137,6 @@ static irqreturn_t fsl_dcu_drm_irq(int irq, void *arg)
 		drm_handle_vblank(dev, 0);
 
 	regmap_write(fsl_dev->regmap, DCU_INT_STATUS, int_status);
-	regmap_write(fsl_dev->regmap, DCU_UPDATE_MODE,
-		     DCU_UPDATE_MODE_READREG);
 
 	return IRQ_HANDLED;
 }