acm: Return a valid buffer

This patch reverts a previous patch trying to fix a memory, even
though I don't think there was any. Now return a valid buffer. All
functions calling this function do free the buffer.

Signed-off-by: Stefan Berger <stefanb@us.ibm.com>

tools/python/xen/lowlevel/acm/acm.c

@@ -68,8 +68,6 @@ static void *__getssid(int domid, uint32_t *buflen)
         goto out2;
     } else {
         *buflen = SSID_BUFFER_SIZE;
-        free(buf);
-        buf = NULL;
         goto out2;
     }
  out2: