net: marvell: fix MVNETA_TX_IN_PRGRS bit number

[ Upstream commit 359f4cdd7d78fdf8c098713b05fee950a730f131 ]

According to Armada XP datasheet bit at 0 position is corresponding for
TxInProg indication.

Fixes: c5aff182 ("net: mvneta: driver for Marvell Armada 370/XP network unit")
Signed-off-by: Maxim Kiselev <bigunclemax@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>