hw/nvme: fix memory leak in nvme_dsm

The iocb (and the allocated memory to hold LBA ranges) leaks if reading
the LBA ranges fails.

Fix this by adding a free and an unref of the iocb.

Reported-by: Coverity (CID 1508281)
Fixes: d7d1474fd8 ("hw/nvme: reimplement dsm to allow cancellation")
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
(cherry picked from commit 4b32319cda)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/nvme/ctrl.c

@@ -2491,6 +2491,9 @@ static uint16_t nvme_dsm(NvmeCtrl *n, NvmeRequest *req)
         status = nvme_h2c(n, (uint8_t *)iocb->range, sizeof(NvmeDsmRange) * nr,
                           req);
         if (status) {
+            g_free(iocb->range);
+            qemu_aio_unref(iocb);
+
             return status;
         }