tracing: Rename max_stack_lock to stack_trace_max_lock

Now that max_stack_lock is a global variable, it requires a naming
convention that is unlikely to collide. Rename it to the same naming
convention that the other stack_trace variables have.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index b4c92ab..eae6548 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -271,7 +271,7 @@
 extern unsigned stack_trace_index[];
 extern struct stack_trace stack_trace_max;
 extern unsigned long stack_trace_max_size;
-extern arch_spinlock_t max_stack_lock;
+extern arch_spinlock_t stack_trace_max_lock;
 
 extern int stack_tracer_enabled;
 void stack_trace_print(void);