iommu/mediatek: Fix unsigned domid comparison with less than zero

Currently the check for domid < 0 is always false because domid
is unsigned. Fix this by casting domid to an int before making
the comparison.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20210204150001.102672-1-colin.king@canonical.com
Addresses-Coverity: ("Unsigned comparison against 0")
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/mtk_iommu.c

@@ -645,7 +645,7 @@ static void mtk_iommu_get_resv_regions(struct device *dev,
 	struct iommu_resv_region *region;
 	int prot = IOMMU_WRITE | IOMMU_READ;
 
-	if (domid < 0)
+	if ((int)domid < 0)
 		return;
 	curdom = data->plat_data->iova_region + domid;
 	for (i = 0; i < data->plat_data->iova_region_nr; i++) {