regulator: da9062: fix suspend_enable/disable preparation

Currently the suspend reg_field maps to the pmic voltage selection bits
and is used during suspend_enabe/disable() and during get_mode(). This
seems to be wrong for both use cases.

Use case one (suspend_enabe/disable):
Those callbacks are used to mark a regulator device as enabled/disabled
during suspend. Marking the regulator enabled during suspend is done by
the LDOx_CONF/BUCKx_CONF bit within the LDOx_CONT/BUCKx_CONT registers.
Setting this bit tells the DA9062 PMIC state machine to keep the
regulator on in POWERDOWN mode and switch to suspend voltage.

Use case two (get_mode):
The get_mode callback is used to retrieve the active mode state. Since
the regulator-setting-A is used for the active state and
regulator-setting-B for the suspend state there is no need to check
which regulator setting is active.

Fixes: 4068e518 ("regulator: da9062: DA9062 regulator driver")
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
Link: https://lore.kernel.org/r/20190917124246.11732-2-m.felsch@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>