regulator: Fix regulator_get_error_flags() signature mismatch

The function signature of does not match regulator_get_error_flags()
when CONFIG_REGULATOR is not defined vs. when it is not defined.
This makes both declarations match to prevent compiler errors.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Mark Brown <broonie@kernel.org>