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 <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/usb/em28xx/em28xx.h

···
 	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,