x86: reduce forbid_dac's visibility

It's not used anywhere outside its declaring file.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
index 8467ec2..702714b 100644
--- a/arch/x86/kernel/pci-dma.c
+++ b/arch/x86/kernel/pci-dma.c
@@ -9,8 +9,7 @@
 #include <asm/calgary.h>
 #include <asm/amd_iommu.h>
 
-int forbid_dac __read_mostly;
-EXPORT_SYMBOL(forbid_dac);
+static int forbid_dac __read_mostly;
 
 const struct dma_mapping_ops *dma_ops;
 EXPORT_SYMBOL(dma_ops);
diff --git a/include/asm-x86/dma-mapping.h b/include/asm-x86/dma-mapping.h
index a1a4dc7..c2ddd3d 100644
--- a/include/asm-x86/dma-mapping.h
+++ b/include/asm-x86/dma-mapping.h
@@ -14,7 +14,6 @@
 extern int iommu_merge;
 extern struct device fallback_dev;
 extern int panic_on_overflow;
-extern int forbid_dac;
 extern int force_iommu;
 
 struct dma_mapping_ops {