*: use void * for printing pointers

On higher warning levels, compilers expect %p printf arguments to be
void *.  Since format string / argument warnings can be useful
otherwise, let's get rid of this noise by sprinkling casts to void *
over printf calls.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/ospf6d/ospf6_spf.c b/ospf6d/ospf6_spf.c
index 47a655c..88e1285 100644
--- a/ospf6d/ospf6_spf.c
+++ b/ospf6d/ospf6_spf.c
@@ -639,7 +639,7 @@
     {
       if (IS_OSPF6_DEBUG_SPF(PROCESS) || IS_OSPF6_DEBUG_SPF (TIME))
         zlog_debug ("SPF: calculation timer is already scheduled: %p",
-                   ospf6->t_spf_calc);
+                    (void *)ospf6->t_spf_calc);
       return;
     }