x86: provide a bad_dma_address symbol for i386

It's initially 0, since we don't expect any DMA there.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/include/asm-x86/dma-mapping.h b/include/asm-x86/dma-mapping.h
index c671a0a..984935d 100644
--- a/include/asm-x86/dma-mapping.h
+++ b/include/asm-x86/dma-mapping.h
@@ -10,6 +10,8 @@
 #include <asm/io.h>
 #include <asm/swiotlb.h>
 
+extern dma_addr_t bad_dma_address;
+
 struct dma_mapping_ops {
 	int             (*mapping_error)(dma_addr_t dma_addr);
 	void*           (*alloc_coherent)(struct device *dev, size_t size,