Fix inconsistent IS_ERR and PTR_ERR in tcan4x5x_parse_config().

The proper pointer to be passed as argument is tcan4x5x->device_wake_gpio.

This bug was detected with the help of Coccinelle.

Fixes: 2de49735 ("can: tcan45x: Make wake-up GPIO an optional GPIO")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>