mmu-hash*: Don't update PTE flags when permission is denied

mmu-hash*: Don't update PTE flags when permission is denied

BEHAVIOUR CHANGE

Currently if ppc_hash{32,64}_translate() finds a PTE matching the given
virtual address, it will always update the PTE's R & C (Referenced and
Changed) bits.  This happens even if the PTE's permissions mean we are
about to deny the translation.

This is clearly a bug, although we get away with it because:
  a) It will only incorrectly set, never reset the bits, which should not
cause guest correctness problems.
  b) Linux guests never use the R & C bits anyway.

This patch fixes the behaviour, only updating R & C when access is granted
by the PTE.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>