net: ethernet: ti: cpsw: drop cpsw_tx_packet_submit()

Drop unnecessary wrapper function cpsw_tx_packet_submit() which is used
only in one place.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>