regulator: lp872x: Make REGULATOR_LP872X depend on I2C rather than I2C=y

lp872x regulator driver can be built a module after commit 631a1fc
"regulator: build: Allow most regulators to be built as modules".
Make REGULATOR_LP872X depend on I2C to allow building lp872x module when I2C=m.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
diff --git a/drivers/regulator/Kconfig b/drivers/regulator/Kconfig
index 445b40c..37f697d 100644
--- a/drivers/regulator/Kconfig
+++ b/drivers/regulator/Kconfig
@@ -201,7 +201,7 @@
 
 config REGULATOR_LP872X
 	tristate "TI/National Semiconductor LP8720/LP8725 voltage regulators"
-	depends on I2C=y
+	depends on I2C
 	select REGMAP_I2C
 	help
 	  This driver supports LP8720/LP8725 PMIC