See upstream commit:
Author: Jeff Mahoney <jeffm@suse.com>
Date: Wed Jun 28 21:56:54 2017 -0600
btrfs: constify tracepoint arguments
Tracepoint arguments are all read-only. If we mark the arguments
as const, we're able to keep or convert those arguments to const
where appropriate.
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>