x86/ibt,ftrace: Annotate ftrace code patching

These are code patching sites, not indirect targets.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154318.936599479@infradead.org