exec: fix memory leak in find_max_supported_pagesize()

exec: fix memory leak in find_max_supported_pagesize()

The string returned by object_property_get_str() is dynamically allocated.

Signed-off-by: Greg Kurz <groug@kaod.org>
Message-Id: <152231458624.69730.1752893648612848392.stgit@bahia.lan>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
(cherry picked from commit 72a841d2a403b56ff894fa007b172dc9bcb3dae8)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>