net: stmmac: Assign configured channel value to EXTTS event

Assign the configured channel value to the EXTTS event in the timestamp
interrupt handler. Without assigning the correct channel, applications
like ts2phc will refuse to accept the event, resulting in errors such
as:
...
ts2phc[656.834]: config item end1.ts2phc.pin_index is 0
ts2phc[656.834]: config item end1.ts2phc.channel is 3
ts2phc[656.834]: config item end1.ts2phc.extts_polarity is 2
ts2phc[656.834]: config item end1.ts2phc.extts_correction is 0
...
ts2phc[656.862]: extts on unexpected channel
ts2phc[658.141]: extts on unexpected channel
ts2phc[659.140]: extts on unexpected channel

Fixes: f4da5652 ("net: stmmac: Add support for external trigger timestamping")
Cc: stable@vger.kernel.org
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Wojciech Drewek <wojciech.drewek@intel.com>
Link: https://lore.kernel.org/r/20240618073821.619751-1-o.rempel@pengutronix.de


Signed-off-by: Paolo Abeni <pabeni@redhat.com>