regulator: hi6421v600: Fix getting wrong drvdata that causes boot failure

Since config.dev = pdev->dev.parent in current code, so
dev_get_drvdata(rdev->dev.parent) actually returns the drvdata of the mfd
device rather than the regulator. Fix it.

Fixes: 9bc146ac ("regulator: hi6421v600: Fix setting wrong driver_data")
Reported-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210630074246.2305166-1-axel.lin@ingics.com


Signed-off-by: Mark Brown <broonie@kernel.org>