this_cpu: Use this_cpu_xx in trace_functions_graph.c

ftrace_cpu_disabled usage in trace_functions_graph.c were left out
during this_cpu_xx conversion in commit 9288f99a

 causing compile
failure.  Convert them.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Christoph Lameter <cl@linux-foundation.org>