qdev: Check dev->realized at set_size()

qdev: Check dev->realized at set_size()

This setter is one of the very few property setters that don't
check dev->realized, and there's no reason to make size
properties different from the rest.  Add the missing check.

Fixes: e8cd45c78f53 ("qdev: Add SIZE type to qdev properties")
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20201211220529.2290218-5-ehabkost@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>