iommu/vt-d: Use right Kconfig option name

The CONFIG_ prefix should be added in the code.

Fixes: 04618252 ("iommu/vt-d: Add Kconfig option to enable/disable scalable mode")
Reported-and-tested-by: Kumar, Sanjay K <sanjay.k.kumar@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Cc: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/20200501072427.14265-1-baolu.lu@linux.intel.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -371,11 +371,11 @@ int dmar_disabled = 0;
 int dmar_disabled = 1;
 #endif /* CONFIG_INTEL_IOMMU_DEFAULT_ON */
 
-#ifdef INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
+#ifdef CONFIG_INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
 int intel_iommu_sm = 1;
 #else
 int intel_iommu_sm;
-#endif /* INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON */
+#endif /* CONFIG_INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON */
 
 int intel_iommu_enabled = 0;
 EXPORT_SYMBOL_GPL(intel_iommu_enabled);