Clean up some -pedantic warnings about passing non-void-pointers with %p.

Clean up some -pedantic warnings about passing non-void-pointers with %p.

src/dict-splay.c (dict_sanity_check_node): Cast struct pointers to void*
    when passing them to snprintf().
src/helpfile.c (vsend_message): Likewise for log_module().
src/mod-sockcheck.c (sockcheck_free_client): Likewise.
  (sockcheck_print_client): Likewise.
  (sockcheck_elaborate_state): Likewise.
  (sockcheck_advance): Likewise.
  (sockcheck_begin_test): Likewise.
  (sockcheck_start_client): Likewise.
src/proto-p10.c (AddUser): Likewise.
src/sar.c (sar_fd_readable): Likewise.
  (sar_getaddr_append): Likewise.