powerpc/pseries/iommu: Fix set but not used values

The commit b7d6bf4f ("powerpc/pseries/pci: Remove obsolete SW
invalidate") left 2 variables unused.

  arch/powerpc/platforms/pseries/iommu.c:108:17: warning: variable 'tces' set but not used
    __be64 *tcep, *tces;
                   ^~~~

  arch/powerpc/platforms/pseries/iommu.c:132:17: warning: variable 'tces' set but not used
    __be64 *tcep, *tces;
                   ^~~~

Also, the commit 68c0449e ("powerpc/pseries/iommu: Use memory@
nodes in max RAM address calculation") set "ranges" in
ddw_memory_hotplug_max() but never use it.

  arch/powerpc/platforms/pseries/iommu.c: In function 'ddw_memory_hotplug_max':
  arch/powerpc/platforms/pseries/iommu.c:948:7: warning: variable 'ranges' set but not used
     int ranges, n_mem_addr_cells, n_mem_size_cells, len;
         ^~~~~~

Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>