sunvnet: remove unused variable in maybe_tx_wakeup

The vio_dring_state *dr variable is unused in maybe_tx_wakeup().
As the comments indicate, we call maybe_tx_wakeup() whenever we
get a STOPPED LDC message on the port. If the queue is stopped,
we want to wake it up so that we will send another START message
at the next TX and trigger the consumer to drain the dring.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>