regulator: vqmmc-ipq4019: Trivial clean up

A few trivial clean up:
* Make ipq4019_regulator_voltage_ops and vmmc_regulator const
* Make ipq4019_vmmcq_regmap_config static
* Use regulator_map_voltage_ascend

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20200114065847.31667-2-axel.lin@ingics.com


Signed-off-by: Mark Brown <broonie@kernel.org>