regulator: tps6507x - add missing platform_set_drvdata in tps6507x_pmic_probe

We should call platform_set_drvdata() before calling platform_get_drvdata().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>