ftrace: fix building with SYSCTL=y but DYNAMIC_FTRACE=n

ftrace: fix building with SYSCTL=y but DYNAMIC_FTRACE=n

Ok so hopefully this is the last of it. 0day picked up a build
failure [0] when SYSCTL=y but DYNAMIC_FTRACE=n. This can be fixed
by just declaring an empty routine for the calls moved just
recently.

[0] https://lkml.kernel.org/r/202204161203.6dSlgKJX-lkp@intel.com

Reported-by: kernel test robot <lkp@intel.com>
Fixes: f8b7d2b4c192 ("ftrace: fix building with SYSCTL=n but DYNAMIC_FTRACE=y")
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>