ftrace: Have function graph tracer use global_ops for filtering

Commit 4104d326

 "ftrace: Remove global function list and call
function directly" cleaned up the global_ops filtering and made
the code simpler. But it left out function graph filtering which
also depended on that code. The function graph filtering still
needs to use global_ops as the filter otherwise it wont filter
at all.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>