drivers: nxp_enet: Fix tx error handling

The code path for error handling and timestamping in tx path
was meant to be identical in function to old eth_mcux driver,
but there is actually a discrepancy causing no error handling
for timestamped frames, fix it.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>
(cherry picked from commit b29190c3)