memory: as_update_topology_pass: Improve comments

memory: as_update_topology_pass: Improve comments

These comments were a little difficult to read. First one had
incorrect parenthesis. The part about attributes changing is
really applicable to the region being 'in both' rather than 'in
new'

Second comment has an obscure parenthetic about 'Logging may have
changed'. Made clearer, as this if is supposed to handle the case where
the memory region is unchanged (with the notable exception re logging).

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>