s390/mm: no need for pte_alloc_map_lock() if we know the pmd is present

pte_map_lock() is sufficient.

Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Link: https://lore.kernel.org/r/20210909162248.14969-8-david@redhat.com


Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>