regulator: core: Fix exported symbols to the exported GPL version

Change the exported symbols introduced by commit e9153311
("regulator: vctrl-regulator: Avoid deadlock getting and setting the voltage")
from EXPORT_SYMBOL() to EXPORT_SYMBOL_GPL(), like is used for all the core
parts.

Fixes: e9153311 ("regulator: vctrl-regulator: Avoid deadlock getting and setting the voltage")
Reported-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Link: https://lore.kernel.org/r/20200120123921.1204339-1-enric.balletbo@collabora.com


Signed-off-by: Mark Brown <broonie@kernel.org>