davinci_mdio: Fix MDIO timeout check

davinci_mdio: Fix MDIO timeout check

commit 5b76d0600b2b08eef77f8e9226938b7b6bde3099 upstream.

Under heavy load (flood ping) it is possible for the MDIO timeout to
expire before the loop checks the GO bit again. This patch adds an
additional check whether the operation was done before actually
returning -ETIMEDOUT.

To reproduce this bug, flood ping the device, e.g., ping -f -l 1000
After some time, a "timed out waiting for user access" warning
may appear. And even worse, link may go down since the PHY reported a
timeout.

Signed-off-by: Christian Riesch <christian.riesch@omicron.at>
Cc: Cyril Chemparathy <cyril@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>