net: marvell: fix MVNETA_TX_IN_PRGRS bit number

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>