Revert "dma-mapping: clear dev->dma_ops in arch_teardown_dma_ops"

This reverts commit 46053c73.

This change breaks architectures setting up dma_ops in their own magic
way and not using arch_setup_dma_ops, so revert it.
Reported-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>

arch/arm64/include/asm/dma-mapping.h

@@ -39,6 +39,11 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 			const struct iommu_ops *iommu, bool coherent);
 #define arch_setup_dma_ops	arch_setup_dma_ops
 
+#ifdef CONFIG_IOMMU_DMA
+void arch_teardown_dma_ops(struct device *dev);
+#define arch_teardown_dma_ops	arch_teardown_dma_ops
+#endif
+
 /* do not use this function in a driver */
 static inline bool is_device_dma_coherent(struct device *dev)
 {

arch/arm64/mm/dma-mapping.c

@@ -862,6 +862,11 @@ static void __iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 		 dev_name(dev));
 }
 
+void arch_teardown_dma_ops(struct device *dev)
+{
+	dev->dma_ops = NULL;
+}
+
 #else
 
 static void __iommu_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,

include/linux/dma-mapping.h

@@ -665,10 +665,7 @@ static inline void arch_setup_dma_ops(struct device *dev, u64 dma_base,
 #endif
 
 #ifndef arch_teardown_dma_ops
-static inline void arch_teardown_dma_ops(struct device *dev)
-{
-	dev->dma_ops = NULL;
-}
+static inline void arch_teardown_dma_ops(struct device *dev) { }
 #endif
 
 static inline unsigned int dma_get_max_seg_size(struct device *dev)