qemu: Fix virFileMakePath error handling in snapshot creation

virFileMakePath returns an errno value on error, that will never
be negative. An virFileMakePath error would have been ignored here,
instead of being reported correctly.

src/qemu/qemu_driver.c

@@ -7498,7 +7498,7 @@ static int qemuDomainSnapshotWriteMetadata(virDomainObjPtr vm,
         goto cleanup;
     }
     err = virFileMakePath(snapDir);
-    if (err < 0) {
+    if (err != 0) {
         virReportSystemError(err, _("cannot create snapshot directory '%s'"),
                              snapDir);
         goto cleanup;