libcamera: V4L2BufferCache: Mark Entry::operator==() as const

The comparison operator does not change any state, mark it as const.

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

src/libcamera/include/v4l2_videodevice.h

@@ -122,7 +122,7 @@ private:
 		Entry();
 		Entry(bool free, const FrameBuffer &buffer);
 
-		bool operator==(const FrameBuffer &buffer);
+		bool operator==(const FrameBuffer &buffer) const;
 
 		bool free;