regulator: Remove all platform_set_drvdata(pdev, NULL) in drivers

Since 0998d063 "device-core: Ensure drvdata = NULL when no driver is bound",
this is done by driver core after device_release or on probe failure.
Thus we can remove all platform_set_drvdata(pdev, NULL) in drivers.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>