iommu_gas: Fix assertion.

placeholder entry end changed to 0 in f591287
("iommu_gas: make placeholder entry at the start of the GAS zero size")

Reviewed by:	kib
Differential Revision:	https://reviews.freebsd.org/D55326

Author: bukinr

sys/dev/iommu/iommu_gas.c

@@ -282,7 +282,7 @@ iommu_gas_fini_domain(struct iommu_domain *domain)
 
 	entry = RB_MIN(iommu_gas_entries_tree, &domain->rb_root);
 	KASSERT(entry->start == 0, ("start entry start %p", domain));
-	KASSERT(entry->end == IOMMU_PAGE_SIZE, ("start entry end %p", domain));
+	KASSERT(entry->end == 0, ("start entry end %p", domain));
 	KASSERT(entry->flags ==
 	    (IOMMU_MAP_ENTRY_PLACE | IOMMU_MAP_ENTRY_UNMAPPED),
 	    ("start entry flags %p", domain));