net: enetc: remove local "priv" variable in enetc_clean_tx_ring()

The "priv" variable is needed in the "check_writeback" scope since
commit d3982312 ("enetc: add hardware timestamping support").

Since commit 7294380c ("enetc: support PTP Sync packet one-step
timestamping"), we also need "priv" in the larger function scope.

So the local variable from the "if" block scope is not needed, and
actually shadows the other one. Delete it.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>