async_tx: provide __async_inline for HAS_DMA=n archs

To allow an async_tx routine to be compiled away on HAS_DMA=n arch it
needs to be declared __always_inline otherwise the compiler may emit
code and cause a link error.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
diff --git a/include/linux/async_tx.h b/include/linux/async_tx.h
index 45f6297..5fc2ef8 100644
--- a/include/linux/async_tx.h
+++ b/include/linux/async_tx.h
@@ -21,6 +21,15 @@
 #include <linux/spinlock.h>
 #include <linux/interrupt.h>
 
+/* on architectures without dma-mapping capabilities we need to ensure
+ * that the asynchronous path compiles away
+ */
+#ifdef CONFIG_HAS_DMA
+#define __async_inline
+#else
+#define __async_inline __always_inline
+#endif
+
 /**
  * dma_chan_ref - object used to manage dma channels received from the
  *   dmaengine core.