platform_get_resource() may fail and return NULL, so we should
better check it's return value to avoid a NULL pointer dereference
a bit later in the code.

This is detected by Coccinelle semantic patch.

Fixes: 911a8882 ("memory: jz4780-nemc: driver for the NEMC on JZ4780 SoCs")
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Acked-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/1607070717-32880-1-git-send-email-zhangchangzhong@huawei.comSigned-off-by: Krzysztof Kozlowski <krzk@kernel.org>