tracefs: Annotate tracefs_ops with __ro_after_init

tracefs: Annotate tracefs_ops with __ro_after_init

tracefs_ops is initialized inside tracefs_create_instance_dir and not
modified after. tracefs_create_instance_dir allows for initialization
only once, and is called from create_trace_instances(marked __init),
which is called from tracer_init_tracefs(marked __init). Also, mark
tracefs_create_instance_dir as __init.

Link: http://lkml.kernel.org/r/[email protected]
Reviewed-by: Kees Cook <[email protected]>
Signed-off-by: Zubin Mithra <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>