s390x/mmu: Renaming related to the ASCE confusion

s390x/mmu: Renaming related to the ASCE confusion

An Address Space Control Element (ASCE) is only the very first unit of
an s390 address translation (normally residing in one of the control
registers). The entries in the page tables are called differently.
So let's call the relevant variable pt_entry instead of asce in
mmu_translate_pte() to avoid future confusion (thus there is no
functional change in this patch, just renaming).

Signed-off-by: Thomas Huth <[email protected]>
Signed-off-by: Jens Freimann <[email protected]>
Reviewed-by: Cornelia Huck <[email protected]>
Signed-off-by: Christian Borntraeger <[email protected]>