can: j1939: j1939_session_completed(): use consistent name se_skb for the session skb

can: j1939: j1939_session_completed(): use consistent name se_skb for the session skb

This patch changes the name of the "skb" variable in
j1939_session_completed() to "se_skb" as it's the session skb. The
same name is used in other functions for the session skb.

Cc: Robin van der Gracht <robin@protonic.nl>
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/r/20210616102811.2449426-4-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>