siox: bus-gpio: Simplify using devm_siox_* functions

With the devm variant of siox_master_allocate() and
siox_master_register() the remove callback can be dropped. This also
simplifies the error paths in the probe function.

Acked-by: Thorsten Scherer <t.scherer@eckelmann.de>
Link: https://lore.kernel.org/r/e3c598de536deadc7efef9c21ccb49d31eb240a9.1708328466.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>