selinux: fix a possible memory leak in cond_read_node()

The cond_read_node() should free the given node on error path as it's
not linked to p->cond_list yet.  This is done via cond_node_destroy()
but it's not called when next_entry() fails before the expr loop.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Paul Moore <pmoore@redhat.com>