s390x/mmu: Clean up mmu_translate_asc()

s390x/mmu: Clean up mmu_translate_asc()

We can get rid of the switch(asc) in mmu_translate_asc() by simply
selecting the right control register ASCE in the mmu_translate()
function already.
This patch is based on an original patch/idea by Ralf Hoppe.

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