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>

arch/x86/kernel/amd_iommu_init.c

@@ -801,8 +801,10 @@ void __init amd_iommu_detect(void)
 
 	if (acpi_table_parse("IVRS", early_amd_iommu_detect) == 0) {
 		iommu_detected = 1;
+#ifdef CONFIG_GART_IOMMU
 		gart_iommu_aperture_disabled = 1;
 		gart_iommu_aperture = 0;
+#endif
 	}
 }