media: cx231xx/cx231xx.h: Remove repeated struct declaration

struct cx231xx is declared at 146th line.
The declaration here is unnecessary. Remove it.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/usb/cx231xx/cx231xx.h

@@ -425,8 +425,6 @@ struct cx231xx_audio {
 	u16 end_point_addr;
 };
 
-struct cx231xx;
-
 /*****************************************************************/
 /* set/get i2c */
 /* 00--1Mb/s, 01-400kb/s, 10--100kb/s, 11--5Mb/s */