can: etas_es58x: use error pointer during device probing

Make es58x_init_es58x_dev return a pointer to the allocated structure
instead of returning an integer. Errors are handled through the helper
function ERR_PTR and IS_ERR.

This slightly simplifies the code.

Link: https://lore.kernel.org/r/20210628155420.1176217-3-mailhol.vincent@wanadoo.fr


Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>