intel-iommu: Fix one last ia64 build problem in Pass Through Support

On ia64 with CONFIG_DMAR=n and CONFIG_SWIOTLB=y (as used in
arch/ia64/configs/tiger_defconfig) there is still a link
error with iommu_pass_through listed as an undefined symbol:

arch/ia64/kernel/built-in.o: In function `pci_swiotlb_init':
(.init.text+0x7f70): undefined reference to `iommu_pass_through'

Fix it by #defining iommu_pass_through away in asm/iommu.h
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

arch/ia64/include/asm/iommu.h

@@ -9,7 +9,11 @@ extern void pci_iommu_shutdown(void);
 extern void no_iommu_init(void);
 extern int force_iommu, no_iommu;
 extern int iommu_detected;
+#ifdef	CONFIG_DMAR
 extern int iommu_pass_through;
+#else
+#define iommu_pass_through	(0)
+#endif
 extern void iommu_dma_init(void);
 extern void machvec_init(const char *name);