regulator: isl9305: REGULATOR_ISL9305 needs to select REGMAP_I2C

Fix ERROR: "devm_regmap_init_i2c" [drivers/regulator/isl9305.ko] undefined!
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/Kconfig

@@ -253,6 +253,7 @@ config REGULATOR_HI6421
 config REGULATOR_ISL9305
 	tristate "Intersil ISL9305 regulator"
 	depends on I2C
+	select REGMAP_I2C
 	help
 	  This driver supports ISL9305 voltage regulator chip.