staging: fsl-dpaa2/eth: Don't account SWA in tx_data_offset

When configuring the Tx buffer layout, the software annotation size is
mentioned, and MC accounts for it when configuring the frame
tx_data_offset. No need to handle it in the driver as well.

This results in 64B less memory allocated per frame.

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>