regulator: export of_get_regulator_init_data

of_get_regulator_init_data is called in drivers/regulator/fixed.c
which could be a module.

Export of_get_regulator_init_data to fix below build error:
ERROR: "of_get_regulator_init_data" [drivers/regulator/fixed.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>