This patch fixes a typo in the j1939_session_tx_dat() function.

Link: https://lore.kernel.org/r/20210729113917.1655492-1-mkl@pengutronix.de
Fixes: 9d71dd0c ("can: add support of SAE J1939 protocol")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>