signal: make legacy_queue() return bool

legacy_queue() already behaves like a boolean function.  Let's actually
declare it as such too.

Link: http://lkml.kernel.org/r/20180602103653.18181-16-christian@brauner.io
Signed-off-by: Christian Brauner <christian@brauner.io>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: James Morris <james.morris@microsoft.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -972,7 +972,7 @@ static void complete_signal(int sig, struct task_struct *p, int group)
 	return;
 }
 
-static inline int legacy_queue(struct sigpending *signals, int sig)
+static inline bool legacy_queue(struct sigpending *signals, int sig)
 {
 	return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
 }