stacktrace: Get rid of unneeded '!!' pattern

My commit b0c51f1 ("stacktrace: Don't skip first entry on
noncurrent tasks") adds one or zero to skipnr by "!!(current == tsk)".

But the C99 standard says:

  The == (equal to) and != (not equal to) operators are
  ...
  Each of the operators yields 1 if the specified relation is true and 0
  if it is false.

So there is no need to prepend the above expression by "!!" -- remove it.

Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20191111092647.27419-1-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/stacktrace.c

@@ -142,7 +142,7 @@ unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store,
 		.store	= store,
 		.size	= size,
 		/* skip this function if they are tracing us */
-		.skip	= skipnr + !!(current == tsk),
+		.skip	= skipnr + (current == tsk),
 	};
 
 	if (!try_get_task_stack(tsk))
@@ -300,7 +300,7 @@ unsigned int stack_trace_save_tsk(struct task_struct *task,
 		.entries	= store,
 		.max_entries	= size,
 		/* skip this function if they are tracing us */
-		.skip	= skipnr + !!(current == task),
+		.skip	= skipnr + (current == task),
 	};
 
 	save_stack_trace_tsk(task, &trace);