regulator: gpio-regulator: do not pass drvdata pointer as reference

Commit c172708d (regulator: core: Use a struct to pass in
regulator runtime configuration) added the drvdata pointer
only per reference to the new config array in the gpio-regulator.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>