iommu/mediatek: Check return value after calling platform_get_resource()

platform_get_resource() may return NULL pointer, we need check its
return value to avoid null-ptr-deref in resource_size().

Fixes: 42d57fc58aeb ("iommu/mediatek: Initialise/Remove for multi bank dev")
Signed-off-by: Yang Yingliang <[e-mail]>
Reviewed-by: Matthias Brugger <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/mtk_iommu.c

···
 
 	banks_num = data->plat_data->banks_num;
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -EINVAL;
 	if (resource_size(res) < banks_num * MTK_IOMMU_BANK_SZ) {
 		dev_err(dev, "banknr %d. res %pR is not enough.\n", banks_num, res);
 		return -EINVAL;