[media] adv7604: fix tx 5v detect regression

The 5 volt detect functionality broke in 3.14: the code reads IO register 0x70
again after it has already been cleared. Instead it should use the cached
irq_reg_0x70 value and the io_write to 0x71 to clear 0x70 can be dropped since
this has already been done.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: <stable@vger.kernel.org>      # for v3.14 and up
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/i2c/adv7604.c

@@ -1960,10 +1960,9 @@ static int adv76xx_isr(struct v4l2_subdev *sd, u32 status, bool *handled)
 	}
 
 	/* tx 5v detect */
-	tx_5v = io_read(sd, 0x70) & info->cable_det_mask;
+	tx_5v = irq_reg_0x70 & info->cable_det_mask;
 	if (tx_5v) {
 		v4l2_dbg(1, debug, sd, "%s: tx_5v: 0x%x\n", __func__, tx_5v);
-		io_write(sd, 0x71, tx_5v);
 		adv76xx_s_detect_tx_5v_ctrl(sd);
 		if (handled)
 			*handled = true;