powerpc/dma: remove unnecessary BUG()

Direction is already checked in all calling functions in
include/linux/dma-mapping.h and also in called function __dma_sync()

So really no need to check it once more here.
Signed-off-by: NChristophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/dma.c

@@ -235,8 +235,6 @@ static inline dma_addr_t dma_nommu_map_page(struct device *dev,
 					     enum dma_data_direction dir,
 					     unsigned long attrs)
 {
-	BUG_ON(dir == DMA_NONE);
-
 	if (!(attrs & DMA_ATTR_SKIP_CPU_SYNC))
 		__dma_sync_page(page, offset, size, dir);