regulator: lp872x: Depend on I2C=y

Kconfig doesn't do the right thing for us here.
Reported-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/Kconfig

@@ -234,7 +234,7 @@ config REGULATOR_LP3972
 
 config REGULATOR_LP872X
 	bool "TI/National Semiconductor LP8720/LP8725 voltage regulators"
-	depends on I2C
+	depends on I2C=y
 	select REGMAP_I2C
 	help
 	  This driver supports LP8720/LP8725 PMIC