net: ethernet: ti: cpsw: fix cpsw assignment in resume

There is a copy-paste error, which hides breaking of resume
for CPSW driver: there was replaced netdev_priv() to ndev_to_cpsw(ndev)
in suspend, but left it unchanged in resume.

Fixes: 606f3993
(ti: cpsw: move platform data and slaves info to cpsw_common)

Reported-by: Alexey Starikovskiy <AStarikovskiy@topcon.com>
Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>