reset: amlogic: aux: get regmap through parent device

Get regmap directly from the parent device registering the
auxiliary reset driver, instead of using device data attached
to the auxiliary device.

This simplifies the registration a bit.

Suggested-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20241209-meson-rst-aux-rework-v1-1-d2afb69cc72e@baylibre.com


Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>