include: ll_schedule_domain: Fix struct comp_dev related warnings

Declare struct comp_dev to avoid warnings if ll_schedule_domain.h is
included before struct comp_dev is defined.

Signed-off-by: Jyri Sarha <jyri.sarha@linux.intel.com>

Author: Jyri Sarha

src/include/sof/schedule/ll_schedule_domain.h

@@ -35,6 +35,7 @@ struct dma;
 struct ll_schedule_domain;
 struct task;
 struct timer;
+struct comp_dev;
 
 struct ll_schedule_domain_ops {
 	int (*domain_register)(struct ll_schedule_domain *domain,