hmp_info_memdev && hmp_info_memory_devices were missing
hmp_handle_error calls.  Add them.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170817104216.29150-2-dgilbert@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>