hw/ssi/pnv_spi: Fixes Coverity CID 1558831

hw/ssi/pnv_spi: Fixes Coverity CID 1558831

In this commit the following coverity scan defect has been fixed
CID 1558831:  Resource leaks  (RESOURCE_LEAK)
  Variable "rsp_payload" going out of scope leaks the storage it
  points to.

Cc: qemu-stable@nongnu.org
Fixes: Coverity CID 1558831
Signed-off-by: Chalapathi V <chalapathi.v@linux.ibm.com>
Fixes: b4cb930e40 ("hw/ssi: Extend SPI model")
[PMD: Rebased on previous commit (returning earlier)]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>