stacktrace: cleanup inconsistent variable type

Modify the variable type of 'skip' member of struct stack_trace.
In theory, the 'skip' variable type should be unsigned int.
There are two reasons:
- The 'skip' only has two situation, 1)Positive value, 2)Zero
- The 'skip' of struct stack_trace has inconsistent type with struct
  stack_trace_data, it makes a bit confusion in the relationship between
  struct stack_trace and stack_trace_data.

Signed-off-by: Walter Wu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>
Cc: Matthias Brugger <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

Author: truhuan

include/linux/stacktrace.h

@@ -64,7 +64,7 @@ void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
 struct stack_trace {
 	unsigned int nr_entries, max_entries;
 	unsigned long *entries;
-	int skip;	/* input argument: How many entries to skip */
+	unsigned int skip;	/* input argument: How many entries to skip */
 };
 
 extern void save_stack_trace(struct stack_trace *trace);