tree: fix mem leak in list-subsys verbose option

Valgrind revealed a mem leak while running nvme list-subsys -vv:

==2486== 18 bytes in 1 blocks are still reachable in loss record 1 of 1
==2486==    at 0x4841984: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2486==    by 0x4956037: __vasprintf_internal (in /lib64/libc.so.6)
==2486==    by 0x49F73AE: __asprintf_chk (in /lib64/libc.so.6)
==2486==    by 0x49796FB: strerror_l (in /lib64/libc.so.6)
==2486==    by 0x488A4AF: nvme_scan_topology (tree.c:317)
==2486==    by 0x42E3BC: list_subsys (nvme.c:3499)
==2486==    by 0x445F88: handle_plugin (plugin.c:190)
==2486==    by 0x407620: main (nvme.c:11119)

Fix this by ensuring an appropriate value is passed to strerror().

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

Author: martin-gpy

libnvme/src/nvme/tree.c

@@ -316,7 +316,7 @@ int nvme_scan_topology(struct nvme_global_ctx *ctx, nvme_scan_filter_t f, void *
 		if (ret < 0) {
 			nvme_msg(ctx, LOG_DEBUG,
 				 "failed to scan subsystem %s: %s\n",
-				 subsys.ents[i]->d_name, strerror(ret));
+				 subsys.ents[i]->d_name, strerror(-ret));
 		}
 	}