x86: remove unused swiotlb_phys_to_bus() and swiotlb_bus_to_phys()

phys_to_dma() and dma_to_phys() are used instead of
swiotlb_phys_to_bus() and swiotlb_bus_to_phys().
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>

arch/x86/kernel/pci-swiotlb.c

@@ -13,16 +13,6 @@
 
 int swiotlb __read_mostly;
 
-dma_addr_t swiotlb_phys_to_bus(struct device *hwdev, phys_addr_t paddr)
-{
-	return paddr;
-}
-
-phys_addr_t swiotlb_bus_to_phys(struct device *hwdev, dma_addr_t baddr)
-{
-	return baddr;
-}
-
 static void *x86_swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 					dma_addr_t *dma_handle, gfp_t flags)
 {