SUNRPC: Kill compiler warning when RPC_DEBUG is unset

Loads of these:

linux/net/sunrpc/rpcb_clnt.c:942:2: warning: suggest braces around
  empty body in ‘do’ statement [-Wempty-body]

show up when I unset CONFIG_PROC_SYSCTL.  Seen with

  gcc (GCC) 4.6.1 20110908 (Red Hat 4.6.1-9)

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>