dma-mapping: remove the dma_mmap_from_dev_coherent export

dma_mmap_from_dev_coherent is only used by dma_map_ops instances,
none of which is modular.
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/coherent.c

@@ -277,7 +277,6 @@ int dma_mmap_from_dev_coherent(struct device *dev, struct vm_area_struct *vma,
 
 	return __dma_mmap_from_coherent(mem, vma, vaddr, size, ret);
 }
-EXPORT_SYMBOL(dma_mmap_from_dev_coherent);
 
 int dma_mmap_from_global_coherent(struct vm_area_struct *vma, void *vaddr,
 				   size_t size, int *ret)