SUNRPC: remove an unneeded NULL check in xprt_connect()

We check "task->tk_rqstp" and then we dereference it without checking on
the next line.  The only caller is call_connect() and that has a check
which prevents it from calling xprt_connect() with a NULL.

                if (task->tk_status < 0)
                        return;

If "task->tk_rqstp" were NULL then "tk_status" would be -EAGAIN.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>