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

lp872x regulator driver can be built a module after commit 631a1fc4
"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: NAxel Lin <axel.lin@ingics.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

drivers/regulator/Kconfig

@@ -201,7 +201,7 @@ config REGULATOR_LP3972
 
 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