regulator: max8893: Select REGMAP_I2C to fix build error

Fix build error if REGMAP_I2C is not set.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/20210622141526.472175-1-axel.lin@ingics.com


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