ftrace: Fix typo in comment

Spelling mistake (triple letters) in comment.
Detected with the help of Coccinelle.

Link: https://lkml.kernel.org/r/20220521111145.81697-81-Julia.Lawall@inria.fr

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>