xlnx-zdma: Correct mem leaks and memset to zero on desc unaligned errors

xlnx-zdma: Correct mem leaks and memset to zero on desc unaligned errors

Coverity found that the string return by 'object_get_canonical_path' was not
being freed at two locations in the model (CID 1391294 and CID 1391293) and
also that a memset was being called with a value greater than the max of a byte
on the second argument (CID 1391286). This patch corrects this by adding the
freeing of the strings and also changing to memset to zero instead on
descriptor unaligned errors.

Signed-off-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180528184859.3530-1-frasse.iglesias@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>