[media] adv7183: fix querystd

If no signal is detected, return V4L2_STD_UNKNOWN. Otherwise AND the standard
with the detected standards.
Note that the v4l2 core initializes the std with tvnorms before calling the
querystd ioctl.
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Scott Jiang <scott.jiang.linux@gmail.com>
Acked-by: Scott Jiang <scott.jiang.linux@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/i2c/adv7183.c

@@ -374,28 +374,28 @@ static int adv7183_querystd(struct v4l2_subdev *sd, v4l2_std_id *std)
 	reg = adv7183_read(sd, ADV7183_STATUS_1);
 	switch ((reg >> 0x4) & 0x7) {
 	case 0:
-		*std = V4L2_STD_NTSC;
+		*std &= V4L2_STD_NTSC;
 		break;
 	case 1:
-		*std = V4L2_STD_NTSC_443;
+		*std &= V4L2_STD_NTSC_443;
 		break;
 	case 2:
-		*std = V4L2_STD_PAL_M;
+		*std &= V4L2_STD_PAL_M;
 		break;
 	case 3:
-		*std = V4L2_STD_PAL_60;
+		*std &= V4L2_STD_PAL_60;
 		break;
 	case 4:
-		*std = V4L2_STD_PAL;
+		*std &= V4L2_STD_PAL;
 		break;
 	case 5:
-		*std = V4L2_STD_SECAM;
+		*std &= V4L2_STD_SECAM;
 		break;
 	case 6:
-		*std = V4L2_STD_PAL_Nc;
+		*std &= V4L2_STD_PAL_Nc;
 		break;
 	case 7:
-		*std = V4L2_STD_SECAM;
+		*std &= V4L2_STD_SECAM;
 		break;
 	default:
 		*std = V4L2_STD_UNKNOWN;