drm/amd/display: remove unnecessary braces to fix coding style

checkpatch complains that:

WARNING: braces {} are not necessary for single statement blocks
+                if (pool->base.irqs != NULL) {
+                        dal_irq_service_destroy(&pool->base.irqs);
+                }

Fixed it by removing unnecessary braces to fix the coding style issue.
Signed-off-by: RutingZhang <u202112078@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/resource/dcn21/dcn21_resource.c

@@ -713,9 +713,8 @@ static void dcn21_resource_destruct(struct dcn21_resource_pool *pool)
 			pool->base.hubps[i] = NULL;
 		}
 
-		if (pool->base.irqs != NULL) {
+		if (pool->base.irqs != NULL)
 			dal_irq_service_destroy(&pool->base.irqs);
-		}
 	}
 
 	for (i = 0; i < pool->base.res_cap->num_ddc; i++) {