regulator: bq257xx: Remove reference to the parent MFD's dev

regulator: bq257xx: Remove reference to the parent MFD's dev

Drop the ->bq field from the platform data of the bq257xx regulator driver,
which was only used to get the regmap of the parent MFD device, and use the
regmap from the regulator_dev instead, slimming down the code a bit.

Acked-by: Mark Brown <broonie@kernel.org>
Tested-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Alexey Charkov <alchark@flipper.net>
Link: https://patch.msgid.link/20260331-bq25792-v6-2-0278fba33eb9@flipper.net
Signed-off-by: Mark Brown <broonie@kernel.org>