python/xc: add missing Py_DECREF() to fix a memory leak

python/xc: add missing Py_DECREF() to fix a memory leak

Python PyList_Append() will increase reference count of the item. We have to
decrease its reference count to let it garbage collected.

We missed the Py_DECREF() for 'cpuinfo_obj' here, thus we have a memory leak.

The memory leak could be easily confirmed by:

  # python
  >>> import xen.lowlevel.xc
  >>> xc = xen.lowlevel.xc.xc()
  >>> for i in range(1000): xc.getcpuinfo(1)

And check the python process memory usage before and after:

  # ps f -o vsize,rss,%mem,size,cmd -p <pid>

Signed-off-by: Zhigang Wang <zhigang.x.wang@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>