mfd: tps65218: Fix reported randconfig error

Reported error was:
  ERROR: "regmap_del_irq_chip" [drivers/mfd/tps65218.ko] undefined!
    when CONFIG_REGMAP_IRQ is not enabled.
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -864,6 +864,7 @@ config MFD_TPS65218
 	depends on I2C
 	select MFD_CORE
 	select REGMAP_I2C
+	select REGMAP_IRQ
 	help
 	  If you say yes here you get support for the TPS65218 series of
 	  Power Management chips.