AMD IOMMU: remove unnecessary ifdef

We try to avoid this type of ifdef and we can safely remove this
ifdef.
Signed-off-by: NFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: NJoerg Roedel <joerg.roedel@amd.com>

arch/x86/kernel/amd_iommu.c

@@ -23,9 +23,7 @@
 #include <linux/debugfs.h>
 #include <linux/scatterlist.h>
 #include <linux/iommu-helper.h>
-#ifdef CONFIG_IOMMU_API
 #include <linux/iommu.h>
-#endif
 #include <asm/proto.h>
 #include <asm/iommu.h>
 #include <asm/gart.h>