gcc-4.6: kernel/*: Fix unused but set warnings

No real bugs I believe, just some dead code.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: andi@firstfloor.org
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/ring_buffer.c

@@ -2985,13 +2985,11 @@ static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
 
 static void rb_advance_iter(struct ring_buffer_iter *iter)
 {
-	struct ring_buffer *buffer;
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct ring_buffer_event *event;
 	unsigned length;
 
 	cpu_buffer = iter->cpu_buffer;
-	buffer = cpu_buffer->buffer;
 
 	/*
 	 * Check if we are at the end of the buffer.