bus: ti-sysc: Use PTR_ERR_OR_ZERO() to simplify code

Fixes coccicheck warning:

drivers/bus/ti-sysc.c:506:1-3: WARNING: PTR_ERR_OR_ZERO can be used

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>