[IA64] Fix warning in dma-mapping.c

arch/ia64/kernel/dma-mapping.c:14: warning: control reaches end of non-void function
arch/ia64/kernel/dma-mapping.c:14: warning: no return statement in function returning non-void

This warning was introduced by commit: 390bd132
	Add dma_debug_init() for ia64
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/dma-mapping.c

@@ -10,7 +10,9 @@ EXPORT_SYMBOL(dma_ops);
 
 static int __init dma_init(void)
 {
-       dma_debug_init(PREALLOC_DMA_DEBUG_ENTRIES);
+	dma_debug_init(PREALLOC_DMA_DEBUG_ENTRIES);
+
+	return 0;
 }
 fs_initcall(dma_init);