regulator: Complain if a voltage range is specified but can't be used

It doesn't make much sense to specify a range of voltages consumers can
use if they haven't been given permission to change the voltage. Log if
this happens, probably the user forgot to specify CHANGE_VOLTAGE.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>