hw/block/nvme: fix resource leak in nvme_dif_rw

If nvme_map_dptr() fails, nvme_dif_rw() will leak the bounce context.
Fix this by using the same error handling as everywhere else in the
function.

Reported-by: Coverity (CID 1451080)
Fixes: 146f720c55 ("hw/block/nvme: end-to-end data protection")
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
Reviewed-by: Gollu Appalanaidu <anaidu.gollu@samsung.com>

hw/block/nvme-dif.c

@@ -432,7 +432,7 @@ uint16_t nvme_dif_rw(NvmeCtrl *n, NvmeRequest *req)
 
     status = nvme_map_dptr(n, &req->sg, mapped_len, &req->cmd);
     if (status) {
-        return status;
+        goto err;
     }
 
     ctx->data.bounce = g_malloc(len);