libcamera: v4l2_videodevice: Downgrade 4CC conversion errors to warnings

Failing to convert between V4L2 and DRM 4CCs indicates something is
likely wrong, but doesn't necessarily prevent the camera from being
usable. It may for instance only limit the number of supported formats.
Downgrade the related log messages from LogError to LogWarning.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/v4l2_videodevice.cpp

@@ -1701,7 +1701,7 @@ PixelFormat V4L2VideoDevice::toPixelFormat(V4L2PixelFormat v4l2Fourcc)
 		 * class. Until we fix the logger, work around it.
 		 */
 		libcamera::_log(__FILE__, __LINE__, _LOG_CATEGORY(V4L2)(),
-				LogError).stream()
+				LogWarning).stream()
 			<< "Unsupported V4L2 pixel format "
 			<< v4l2Fourcc.toString();
 		return PixelFormat();
@@ -1789,7 +1789,8 @@ V4L2PixelFormat V4L2VideoDevice::toV4L2PixelFormat(const PixelFormat &pixelForma
 	 * \todo We can't use LOG() in a static method of a Loggable
 	 * class. Until we fix the logger, work around it.
 	 */
-	libcamera::_log(__FILE__, __LINE__, _LOG_CATEGORY(V4L2)(), LogError).stream()
+	libcamera::_log(__FILE__, __LINE__, _LOG_CATEGORY(V4L2)(),
+			LogWarning).stream()
 		<< "Unsupported V4L2 pixel format " << pixelFormat.toString();
 	return {};
 }