media: imx274: fix frame interval handling

1) the numerator and/or denominator might be 0, in that case
   fall back to the default frame interval. This is per the spec
   and this caused a v4l2-compliance failure.

2) the updated frame interval wasn't returned in the s_frame_interval
   subdev op.
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/i2c/imx274.c

@@ -1235,6 +1235,8 @@ static int imx274_s_frame_interval(struct v4l2_subdev *sd,
 	ret = imx274_set_frame_interval(imx274, fi->interval);
 
 	if (!ret) {
+		fi->interval = imx274->frame_interval;
+
 		/*
 		 * exposure time range is decided by frame interval
 		 * need to update it after frame interval changes
@@ -1730,9 +1732,9 @@ static int imx274_set_frame_interval(struct stimx274 *priv,
 		__func__, frame_interval.numerator,
 		frame_interval.denominator);
 
-	if (frame_interval.numerator == 0) {
-		err = -EINVAL;
-		goto fail;
+	if (frame_interval.numerator == 0 || frame_interval.denominator == 0) {
+		frame_interval.denominator = IMX274_DEF_FRAME_RATE;
+		frame_interval.numerator = 1;
 	}
 
 	req_frame_rate = (u32)(frame_interval.denominator