powerpc: Rename __get_SP() to current_stack_pointer()

Michael points out that __get_SP() is a pretty horrible
function name. Let's give it a better name.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/stacktrace.c

@@ -50,7 +50,7 @@ void save_stack_trace(struct stack_trace *trace)
 {
 	unsigned long sp;
 
-	sp = __get_SP();
+	sp = current_stack_pointer();
 
 	save_context_stack(trace, sp, current, 1);
 }