*: 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/lib/zclient.c b/lib/zclient.c
index 41ecbb6..963c705 100644
--- a/lib/zclient.c
+++ b/lib/zclient.c
@@ -919,7 +919,7 @@
   length -= ZEBRA_HEADER_SIZE;
 
   if (zclient_debug)
-    zlog_debug("zclient 0x%p command 0x%x \n", zclient, command);
+    zlog_debug("zclient 0x%p command 0x%x \n", (void *)zclient, command);
 
   switch (command)
     {