mwl8k: make the tx ring drain status messages somewhat more friendly

Old:
> phy0: timeout waiting for tx rings to drain (9 -> 5 pkts), retrying
> phy0: timeout waiting for tx rings to drain (5 -> 2 pkts), retrying
> phy0: tx rings drained

New:
> phy0: waiting for tx rings to drain (9 -> 5 pkts)
> phy0: waiting for tx rings to drain (5 -> 2 pkts)
> phy0: tx rings drained

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>