tree: update nvme_scan_ctrl() return handling

Copilot identified an issue with the return handling of nvme_scan_ctrl()
which could potentially display a misleading error message by nvme_strerror().
Fix the same.

Signed-off-by: Martin George <[email protected]>

Author: martin-gpy

libnvme/src/nvme/tree.c

@@ -297,9 +297,9 @@ int nvme_scan_topology(struct nvme_global_ctx *ctx, nvme_scan_filter_t f, void *
 		nvme_ctrl_t c;
 
 		ret = nvme_scan_ctrl(ctx, ctrls.ents[i]->d_name, &c);
-		if (!ret) {
+		if (ret < 0) {
 			nvme_msg(ctx, LOG_DEBUG, "failed to scan ctrl %s: %s\n",
-				 ctrls.ents[i]->d_name, nvme_strerror(ret));
+				 ctrls.ents[i]->d_name, nvme_strerror(-ret));
 			continue;
 		}
 	}