tracing/function-graph: x86_64 stack allocation cleanup

Only 24 bytes needs to be reserved on the stack for the function graph
tracer on x86_64.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
LKML-Reference: <20090729085837.GB4998@jolsa.lab.eng.brq.redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

arch/x86/kernel/entry_64.S

@@ -146,7 +146,7 @@ ENTRY(ftrace_graph_caller)
 END(ftrace_graph_caller)
 
 GLOBAL(return_to_handler)
-	subq  $80, %rsp
+	subq  $24, %rsp
 
 	/* Save the return values */
 	movq %rax, (%rsp)
@@ -155,10 +155,10 @@ GLOBAL(return_to_handler)
 
 	call ftrace_return_to_handler
 
-	movq %rax, 72(%rsp)
+	movq %rax, 16(%rsp)
 	movq 8(%rsp), %rdx
 	movq (%rsp), %rax
-	addq $72, %rsp
+	addq $16, %rsp
 	retq
 #endif