Instead of having two has_error fields in QEMUFile & QEMUBufferedFile,
reuse the 1st one.  Notice that the one in buffered_file is only set
after a file operation.
Signed-off-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NAnthony Liguori <aliguori@us.ibm.com>