reset: uniphier-glue: Fix possible null-ptr-deref

It will cause null-ptr-deref when resource_size(res) invoked,
if platform_get_resource() returns NULL.

Fixes: 499fef09 ("reset: uniphier: add USB3 core reset control")
Signed-off-by: Hui Tang <tanghui20@huawei.com>
Reviewed-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Link: https://lore.kernel.org/r/20221114004958.258513-1-tanghui20@huawei.com


Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>