cx25821: remove unused cx25821_video_wakeup() declaration

cx25821_video_wakeup() has been removed since
commit b671ae6b ("[media] cx25821: convert to vb2").

So cx25821_video_wakeup is a unused declaration, remove it.
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/pci/cx25821/cx25821-video.h

@@ -36,9 +36,6 @@ do {									\
 } while (0)
 
 #define FORMAT_FLAGS_PACKED       0x01
-extern void cx25821_video_wakeup(struct cx25821_dev *dev,
-				 struct cx25821_dmaqueue *q, u32 count);
-
 extern int cx25821_start_video_dma(struct cx25821_dev *dev,
 				   struct cx25821_dmaqueue *q,
 				   struct cx25821_buffer *buf,