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>