iommu/vt-d: Remove set but not used variable

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/iommu/intel/iommu.c:5643:27: warning: variable 'last_pfn' set but not used [-Wunused-but-set-variable]
5643 |  unsigned long start_pfn, last_pfn;
     |                           ^~~~~~~~

This variable is never used, so remove it.

Fixes: 2a2b8eaa ("iommu: Handle freelists when using deferred flushing in iommu drivers")
Reported-by: Nkernel test robot <lkp@intel.com>
Signed-off-by: NLu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20201127013308.1833610-1-baolu.lu@linux.intel.comSigned-off-by: NWill Deacon <will@kernel.org>

drivers/iommu/intel/iommu.c

@@ -4948,13 +4948,12 @@ static void intel_iommu_tlb_sync(struct iommu_domain *domain,
 	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
 	unsigned long iova_pfn = IOVA_PFN(gather->start);
 	size_t size = gather->end - gather->start;
-	unsigned long start_pfn, last_pfn;
+	unsigned long start_pfn;
 	unsigned long nrpages;
 	int iommu_id;
 
 	nrpages = aligned_nrpages(gather->start, size);
 	start_pfn = mm_to_dma_pfn(iova_pfn);
-	last_pfn = start_pfn + nrpages - 1;
 
 	for_each_domain_iommu(iommu_id, dmar_domain)
 		iommu_flush_iotlb_psi(g_iommus[iommu_id], dmar_domain,