s390/mm: add missing phys_to_virt translation to page table dumper

The page table dumper walks page table tables without using standard
page table primitives in order to also dump broken entries. However it
currently does not translate physical to virtual addresses before
dereferencing them. Therefore add this missing translation.

Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>