xilinx_emacps: Don't check TXSR_TXCOMPL in xemacps_tx_poll()

xilinx_emacps: Don't check TXSR_TXCOMPL in xemacps_tx_poll()

It doesn't really make sense to stop in xemacps_tx_poll() when
TXSR_TXCOMPL is not set. The logic works the other way round: When a
buffer becomes ready after reading TXSR, there is no reason why we
shouldn't process it. This is similar to xemacps_rx_poll() where
RXSR_FRAMERX isn't checked either.

We do stop when no buffers are available, though. In this case, skip
netif_start_queue() because nothing has changed.

Signed-off-by: Thomas Betker <thomas.betker@rohde-schwarz.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>