SUNRPC: Clean up in rpc_show_tasks

/home/cel/linux/net/sunrpc/clnt.c: In function ‘rpc_show_tasks’:
/home/cel/linux/net/sunrpc/clnt.c:1538: warning:
	signed and unsigned type in conditional expression

This points out another case where a conditional expression returns a
signed value in one arm and an unsigned value in the other.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>