hw/nvme: fix memory leak in fdp ruhid parsing

Coverity reports a memory leak of memory when parsing ruhids at
namespace initialization. Since this is just working memory, not needed
beyond the scope of the functions, fix this by adding a g_autofree
annotation.

Reported-by: Coverity (CID 1507979)
Fixes: 73064edfb864 ("hw/nvme: flexible data placement emulation")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>