tracing/function-return-tracer: call prepare_ftrace_return by registers

Impact: Optimize a bit the function return tracer

This patch changes the calling convention of prepare_ftrace_return to
pass its arguments by register. This will optimize it a bit and
prepare it to support dynamic tracing.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 9a0ac85..f976211 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -1217,12 +1217,9 @@
 	pushl %eax
 	pushl %ecx
 	pushl %edx
-	movl 0xc(%esp), %eax
-	pushl %eax
+	movl 0xc(%esp), %edx
 	lea 0x4(%ebp), %eax
-	pushl %eax
 	call prepare_ftrace_return
-	addl $8, %esp
 	popl %edx
 	popl %ecx
 	popl %eax