signal: Make kill_proc_info static

There are no users outside of signal.c so make the function static so
the compiler and other developers have that information.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

kernel/signal.c

@@ -1318,7 +1318,7 @@ int kill_pid_info(int sig, struct siginfo *info, struct pid *pid)
 	}
 }
 
-int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
+static int kill_proc_info(int sig, struct siginfo *info, pid_t pid)
 {
 	int error;
 	rcu_read_lock();