regulator: Staticize 'regulator_states' array

The 'regulator_states' array is used only in this unit and it is not
exported. Make it static.

This also fixes following sparse warning:
drivers/regulator/of_regulator.c:22:12: warning: symbol 'regulator_states' was not declared. Should it be static?

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>