AMD/IOMMU: address violations of MISRA C:2012 Rule 11.8

Drop an unnecessary cast discarding a const qualifier, to comply with
Rule 11.8. The type of the formal parameter ivhd_block is const
qualified.

No functional change.

Signed-off-by: Maria Celeste Cesario <maria.celeste.cesario@bugseng.com>
Signed-off-by: Simone Ballarin <simone.ballarin@bugseng.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/drivers/passthrough/amd/iommu_acpi.c

@@ -1232,7 +1232,7 @@ static int __init get_last_bdf_ivhd(
     while ( ivhd_block->header.length >=
             (block_length + sizeof(struct acpi_ivrs_de_header)) )
     {
-        ivhd_device = (const void *)((u8 *)ivhd_block + block_length);
+        ivhd_device = (const void *)ivhd_block + block_length;
 
         switch ( ivhd_device->header.type )
         {