dma-direct: remove the cached_kernel_address hook

dma-direct now finds the kernel address for coherent allocations based
on the dma address, so the cached_kernel_address hooks is unused and
can be removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

arch/mips/mm/dma-noncoherent.c

@@ -54,11 +54,6 @@ void *uncached_kernel_address(void *addr)
 	return (void *)(__pa(addr) + UNCAC_BASE);
 }
 
-void *cached_kernel_address(void *addr)
-{
-	return __va(addr) - UNCAC_BASE;
-}
-
 static inline void dma_sync_virt(void *addr, size_t size,
 		enum dma_data_direction dir)
 {