x86/PoD: fix (un)locking after 24772:28edc2b31a9b

That c/s introduced a double unlock on the out-of-memory error path of
p2m_pod_demand_populate().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/mm/p2m-pod.c
+++ b/xen/arch/x86/mm/p2m-pod.c
@@ -1075,6 +1075,7 @@ out_of_memory:
     printk("%s: Out of populate-on-demand memory! tot_pages %" PRIu32 " pod_entries %" PRIi32 "\n",
            __func__, d->tot_pages, p2m->pod.entry_count);
     domain_crash(d);
+    return -1;
 out_fail:
     pod_unlock(p2m);
     return -1;