regulator: core: make regulator_register() EPROBE_DEFER aware

Sometimes it can happen that the regulator_of_get_init_data() can't
retrieve the config due to a not probed device the regulator depends on.
Fix that by checking the return value of of_parse_cb() and return
EPROBE_DEFER in such cases.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Link: https://lore.kernel.org/r/20190917154021.14693-4-m.felsch@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>