drm/amdgpu: remove unnecessary forward declaration

Signed-off-by: Nicolai Hähnle <[e-mail]>
Reviewed-by: Alex Deucher <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Cc: [e-mail]

drivers/gpu/drm/amd/amdgpu/amdgpu.h

···
 	uint32_t		align;
 };
 
-struct amdgpu_sa_bo;
-
 /* sub-allocation buffer */
 struct amdgpu_sa_bo {
 	struct list_head		olist;