regulator: 88pm800: Depend on MFD_88PM800 rather than MFD_88PM800=y

This driver can be built as a module, make it depend on MFD_88PM800.
Otherwise, we are not able to select this driver when MFD_88PM800=m.
Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

drivers/regulator/Kconfig

@@ -66,7 +66,7 @@ config REGULATOR_USERSPACE_CONSUMER
 
 config REGULATOR_88PM800
 	tristate "Marvell 88PM800 Power regulators"
-	depends on MFD_88PM800=y
+	depends on MFD_88PM800
 	help
 	  This driver supports Marvell 88PM800 voltage regulator chips.
 	  It delivers digitally programmable output,