ASoC: sgtl5000: Fix charge pump source assignment

If VDDA != VDDIO and any of them is greater than 3.1V, charge pump
source can be assigned automatically [1].

[1] https://www.nxp.com/docs/en/data-sheet/SGTL5000.pdf

Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Reviewed-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20190719100524.23300-7-oleksandr.suvorov@toradex.com
Signed-off-by: Mark Brown <broonie@kernel.org>