dma-debug: use named initializers for dir2name

Make dir2name a little more readable and maintainable by using
named initializers.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

kernel/dma/debug.c

@@ -144,8 +144,12 @@ static const char *type2name[] = {
 	[dma_debug_resource] = "resource",
 };
 
-static const char *dir2name[4] = { "DMA_BIDIRECTIONAL", "DMA_TO_DEVICE",
-				   "DMA_FROM_DEVICE", "DMA_NONE" };
+static const char *dir2name[] = {
+	[DMA_BIDIRECTIONAL]	= "DMA_BIDIRECTIONAL",
+	[DMA_TO_DEVICE]		= "DMA_TO_DEVICE",
+	[DMA_FROM_DEVICE]	= "DMA_FROM_DEVICE",
+	[DMA_NONE]		= "DMA_NONE",
+};
 
 /*
  * The access to some variables in this macro is racy. We can't use atomic_t