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>

kernel/trace/trace_functions_graph.c

@@ -176,7 +176,7 @@ static int __trace_graph_entry(struct trace_array *tr,
 	struct ring_buffer *buffer = tr->buffer;
 	struct ftrace_graph_ent_entry *entry;
 
-	if (unlikely(local_read(&__get_cpu_var(ftrace_cpu_disabled))))
+	if (unlikely(__this_cpu_read(per_cpu_var(ftrace_cpu_disabled))))
 		return 0;
 
 	event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_ENT,
@@ -240,7 +240,7 @@ static void __trace_graph_return(struct trace_array *tr,
 	struct ring_buffer *buffer = tr->buffer;
 	struct ftrace_graph_ret_entry *entry;
 
-	if (unlikely(local_read(&__get_cpu_var(ftrace_cpu_disabled))))
+	if (unlikely(__this_cpu_read(per_cpu_var(ftrace_cpu_disabled))))
 		return;
 
 	event = trace_buffer_lock_reserve(buffer, TRACE_GRAPH_RET,