can: j1939: j1939_session_tx_dat(): use consistent name se_skcb for session skb control buffer

This patch changes the name of the "skcb" variable in
j1939_session_tx_dat() to "se_skcb" as it's the session skb's control
buffer. The same name is used in other functions for the session skb's
control buffer.

Cc: Robin van der Gracht <robin@protonic.nl>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20210616102811.2449426-5-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>