iommu/mediatek: Drop of_match_ptr to fix -Wunused-const-variable

The of_device_id is included unconditionally by of.h header and used
in the driver as well.  Remove of_match_ptr to fix W=1 compile test
warning with !CONFIG_OF:

    drivers/iommu/mtk_iommu.c:833:34: warning: 'mtk_iommu_of_ids' defined but not used [-Wunused-const-variable=]
      833 | static const struct of_device_id mtk_iommu_of_ids[] = {
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200727181842.8441-1-krzk@kernel.orgSigned-off-by: NJoerg Roedel <jroedel@suse.de>

drivers/iommu/mtk_iommu.c

@@ -843,7 +843,7 @@ static struct platform_driver mtk_iommu_driver = {
 	.remove	= mtk_iommu_remove,
 	.driver	= {
 		.name = "mtk-iommu",
-		.of_match_table = of_match_ptr(mtk_iommu_of_ids),
+		.of_match_table = mtk_iommu_of_ids,
 		.pm = &mtk_iommu_pm_ops,
 	}
 };