net: ethernet: altera: TSE: Remove unneeded dma sync for tx buffers

An explicit dma sync for device directly after mapping as well as an
explicit dma sync for cpu directly before unmapping is unnecessary and
costly on the hotpath. So remove these calls.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>