x86: rename stack_pointer to kernel_trap_sp

Choose a less generic name for such a special case.  Add
a comment explaining the odd use in X86_32.

Change the one user of stack_pointer.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
index 0ca4815..e2095cb 100644
--- a/arch/x86/oprofile/backtrace.c
+++ b/arch/x86/oprofile/backtrace.c
@@ -77,7 +77,7 @@
 x86_backtrace(struct pt_regs * const regs, unsigned int depth)
 {
 	struct frame_head *head = (struct frame_head *)frame_pointer(regs);
-	unsigned long stack = stack_pointer(regs);
+	unsigned long stack = kernel_trap_sp(regs);
 
 	if (!user_mode_vm(regs)) {
 		if (depth)