SUNRPC: RPC program information is stored in unsigned integers

Clean up: When looping over RPC version and procedure numbers, use
unsigned index variables.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>