ARM: 8172/1: Use current_stack_pointer in save_stack_trace_tsk

Use the global current_stack_pointer to get the value of the stack pointer.
This change supports being able to compile the kernel with both gcc and clang.
Signed-off-by: Behan Webster <behanw@converseincode.com>
Reviewed-by: Mark Charlebois <charlebm@gmail.com>
Reviewed-by: Jan-Simon Möller <dl9pf@gmx.de>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/stacktrace.c

@@ -134,12 +134,10 @@ static noinline void __save_stack_trace(struct task_struct *tsk,
 		frame.pc = thread_saved_pc(tsk);
 #endif
 	} else {
-		register unsigned long current_sp asm ("sp");
-
 		/* We don't want this function nor the caller */
 		data.skip += 2;
 		frame.fp = (unsigned long)__builtin_frame_address(0);
-		frame.sp = current_sp;
+		frame.sp = current_stack_pointer;
 		frame.lr = (unsigned long)__builtin_return_address(0);
 		frame.pc = (unsigned long)__save_stack_trace;
 	}