media: atmel-isi: Remote unneeeded forward declaration

Remove an unneeded forward declaration for struct v4l2_async_subdev.
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Tested-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com> # Renesas RZ/G2L SMARC
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/atmel/atmel-isi.h

@@ -121,8 +121,6 @@
 #define ISI_DATAWIDTH_8				0x01
 #define ISI_DATAWIDTH_10			0x02
 
-struct v4l2_async_subdev;
-
 struct isi_platform_data {
 	u8 has_emb_sync;
 	u8 hsync_act_low;