coverity-model: model address_space_read/write

Commit eb7eeb88 ("memory: split address_space_read and
address_space_write", 2015-12-17) made address_space_rw
dispatch to one of address_space_read or address_space_write,
rather than vice versa.

For callers of address_space_read and address_space_write this
causes false positive defects when Coverity sees a length-8 write in
address_space_read and a length-4 (e.g. int*) buffer to read into.
As long as the size of the buffer is okay, this is a false positive.

Reflect the code change into the model.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20170315081641.20588-1-pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>