ideapad-laptop: Depend on BACKLIGHT_CLASS_DEVICE instead of selecting it

Selecting BACKLIGHT_CLASS_DEVICE doesn't guarantee that any of its
dependencies are enabled, and these are complicated. Depending isn't ideal
for configuration UI purposes, but is probably more appropriate here.
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>

drivers/platform/x86/Kconfig

@@ -299,8 +299,8 @@ config IDEAPAD_LAPTOP
 	depends on ACPI
 	depends on RFKILL && INPUT
 	depends on SERIO_I8042
+	depends on BACKLIGHT_CLASS_DEVICE
 	select INPUT_SPARSEKMAP
-	select BACKLIGHT_CLASS_DEVICE
 	help
 	  This is a driver for Lenovo IdeaPad netbooks contains drivers for
 	  rfkill switch, hotkey, fan control and backlight control.