net: rswitch: Fix return value in rswitch_start_xmit()

[ Upstream commit 1aaef863 ]

This .ndo_start_xmit() function should return netdev_tx_t value,
not -ENOMEM. So, fix it.

Fixes: 33f5d733 ("net: renesas: rswitch: Improve TX timestamp accuracy")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>