iommu/mediatek: Fix out-of-range warning with clang

clang-14 notices that a comparison is never true when
CONFIG_PHYS_ADDR_T_64BIT is disabled:

drivers/iommu/mtk_iommu.c:553:34: error: result of comparison of constant 5368709120 with expression of type 'phys_addr_t' (aka 'unsigned int') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
        if (dom->data->enable_4GB && pa >= MTK_IOMMU_4GB_MODE_REMAP_BASE)
                                     ~~ ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Add an explicit check for the type of the variable to skip the check
and the warning in that case.

Fixes: b4dad40 ("iommu/mediatek: Adjust the PA for the 4GB Mode")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210927121857.941160-1-arnd@kernel.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>

Author: arndb

drivers/iommu/mtk_iommu.c

@@ -550,7 +550,9 @@ static phys_addr_t mtk_iommu_iova_to_phys(struct iommu_domain *domain,
 	phys_addr_t pa;
 
 	pa = dom->iop->iova_to_phys(dom->iop, iova);
-	if (dom->data->enable_4GB && pa >= MTK_IOMMU_4GB_MODE_REMAP_BASE)
+	if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT) &&
+	    dom->data->enable_4GB &&
+	    pa >= MTK_IOMMU_4GB_MODE_REMAP_BASE)
 		pa &= ~BIT_ULL(32);
 
 	return pa;