AMD IOMMU: use iommu_device_max_index, fix

include/linux/iommu-helper.h has no header guards, which breaks
sparc64 build. Add them.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Joerg Roedel <joerg.roedel@amd.com>
Cc: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/iommu-helper.h

+#ifndef _LINUX_IOMMU_HELPER_H
+#define _LINUX_IOMMU_HELPER_H
+
 static inline unsigned long iommu_device_max_index(unsigned long size,
 						   unsigned long offset,
 						   u64 dma_mask)
@@ -19,3 +22,5 @@ extern unsigned long iommu_area_alloc(unsigned long *map, unsigned long size,
 				      unsigned long align_mask);
 extern void iommu_area_free(unsigned long *map, unsigned long start,
 			    unsigned int nr);
+
+#endif