net: mvpp2: cls: Fix leaked ethtool_rx_flow_rule

The flow_rule is only used when configuring the classification tables,
and should be free'd once we're done using it. The current code only
frees it in the error path.

Fixes: 90b509b3

 ("net: mvpp2: cls: Add Classification offload support")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>