media: v4l2-common: Reduce warnings about missing V4L2_CID_LINK_FREQ control

When operating a pipeline with a missing V4L2_CID_LINK_FREQ control this
two line warning is printed each time the pipeline is started. Reduce
this excessive logging by only warning once for the missing control.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>

Author: Niklas Söderlund

drivers/media/v4l2-core/v4l2-common.c

@@ -505,10 +505,10 @@ s64 __v4l2_get_link_freq_ctrl(struct v4l2_ctrl_handler *handler,
 
 		freq = div_u64(v4l2_ctrl_g_ctrl_int64(ctrl) * mul, div);
 
-		pr_warn("%s: Link frequency estimated using pixel rate: result might be inaccurate\n",
-			__func__);
-		pr_warn("%s: Consider implementing support for V4L2_CID_LINK_FREQ in the transmitter driver\n",
-			__func__);
+		pr_warn_once("%s: Link frequency estimated using pixel rate: result might be inaccurate\n",
+			     __func__);
+		pr_warn_once("%s: Consider implementing support for V4L2_CID_LINK_FREQ in the transmitter driver\n",
+			     __func__);
 	}
 
 	return freq > 0 ? freq : -EINVAL;