passthrough: remove pointless error checks

map_domain_page() cannot return NULL. And if it could, both instances
changed here would leak memory in such a case.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

xen/drivers/passthrough/vtd/iommu.c

@@ -156,8 +156,6 @@ u64 alloc_pgtable_maddr(struct acpi_drhd_unit *drhd, unsigned long npages)
     if ( !pg )
         return 0;
     vaddr = map_domain_page(page_to_mfn(pg));
-    if ( !vaddr )
-        return 0;
     memset(vaddr, 0, PAGE_SIZE * npages);
 
     iommu_flush_cache_page(vaddr, npages);

xen/include/asm-x86/hvm/svm/amd-iommu-proto.h

@@ -131,8 +131,6 @@ static inline struct page_info* alloc_amd_iommu_pgtable(void)
     if ( pg == NULL )
         return 0;
     vaddr = map_domain_page(page_to_mfn(pg));
-    if ( vaddr == NULL )
-        return 0;
     memset(vaddr, 0, PAGE_SIZE);
     unmap_domain_page(vaddr);
     return pg;