media: em28xx/em28xx.h: Remove duplicate struct declaration

struct em28xx is declared at 219th 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/em28xx/em28xx.h

@@ -628,8 +628,6 @@ struct em28xx_audio {
 	atomic_t       stream_started;	/* stream should be running if true */
 };
 
-struct em28xx;
-
 enum em28xx_i2c_algo_type {
 	EM28XX_I2C_ALGO_EM28XX = 0,
 	EM28XX_I2C_ALGO_EM2800,