regulator: tps65910: check TPS65910_NUM_REGS at build time

Check TPS65910_NUM_REGS at build time instead of silently registering
not all regulators at runtime.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Mark Brown <broonie@kernel.org>