can: cc770: Fix use after free in cc770_tx_interrupt()

This fixes use after free introduced by the last cc770 patch.

Signed-off-by: Andri Yngvason <andri.yngvason@marel.com>
Fixes: 74620123 ("can: cc770: Fix queue stall & dropped RTR reply")
Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>