regulator: Silence build warnings from regulator_can_change_voltage()

Cut down on noise for mainstream users of the API and people doing build
testing by dropping the deprecated flag from regulator_can_change_voltage()
as it triggers even on the EXPORT_SYMBOL_GPL() which affects all builds
rather than just the remaining drivers with calls to it (for which fixes
are currently pending).

The function remains deprecated and is expected to be removed entirely
in v4.8.

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