hmp: Compile hmp_info_spice() only with CONFIG_SPICE It's dead code when CONFIG_SPICE is off. If it wasn't, it would crash dereferencing the null pointer returned by the qmp_query_spice() dummy in qmp.c. Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>