x86, AMD IOMMU, build fix #2

fix:

 arch/x86/kernel/amd_iommu.c: In function ‘amd_iommu_init_dma_ops':
 arch/x86/kernel/amd_iommu.c:940: error: lvalue required as left operand of assignment
 arch/x86/kernel/amd_iommu.c:941: error: lvalue required as left operand of assignment

due to !CONFIG_GART_IOMMU.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
index 134dea1..a1b3856 100644
--- a/arch/x86/kernel/amd_iommu.c
+++ b/arch/x86/kernel/amd_iommu.c
@@ -937,8 +937,10 @@
 	iommu_detected = 1;
 	force_iommu = 1;
 	bad_dma_address = 0;
+#ifdef CONFIG_GART_IOMMU
 	gart_iommu_aperture_disabled = 1;
 	gart_iommu_aperture = 0;
+#endif
 
 	dma_ops = &amd_iommu_dma_ops;