posix-aio-compat: Plug memory leak on paio_init() error path

Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

posix-aio-compat.c

@@ -667,6 +667,7 @@ int paio_init(void)
     s->first_aio = NULL;
     if (qemu_pipe(fds) == -1) {
         fprintf(stderr, "failed to create pipe\n");
+        g_free(s);
         return -1;
     }