ARM/dma-mapping: remove a __arch_page_to_dma #error

The __arch_page_to_dma hook is long gone.
Signed-off-by: Christoph Hellwig <hch@lst.de>

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

@@ -23,10 +23,6 @@ static inline const struct dma_map_ops *get_arch_dma_ops(struct bus_type *bus)
 	return NULL;
 }
 
-#ifdef __arch_page_to_dma
-#error Please update to __arch_pfn_to_dma
-#endif
-
 /*
  * dma_to_pfn/pfn_to_dma/dma_to_virt/virt_to_dma are architecture private
  * functions used internally by the DMA-mapping API to provide DMA