iommu/amd: Make a symbol static

Symbol is only used in that file and can be static.
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd_iommu_init.c

@@ -154,7 +154,7 @@ bool amd_iommu_iotlb_sup __read_mostly = true;
 u32 amd_iommu_max_pasid __read_mostly = ~0;
 
 bool amd_iommu_v2_present __read_mostly;
-bool amd_iommu_pc_present __read_mostly;
+static bool amd_iommu_pc_present __read_mostly;
 
 bool amd_iommu_force_isolation __read_mostly;