milkymist_memcard_realize() leaks an Error object when realization of
its "sd-card" device fails. Quite harmless, since we only ever
realize this once, in milkymist_init() via milkymist_memcard_create().
Plug the leak.
Fixes: 3d0369ba49
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Michael Walle <michael@walle.cc>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200630090351.1247703-10-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
b98e8d1230