uml: kill a kconfig warning

Got this warning from Kconfig:

   boolean symbol INPUT tested for 'm'? test forced to 'n'

because INPUT is tristate, not bool.
Signed-off-by: NWANG Cong <xiyou.wangcong@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Jeff Dike <jdike@addtoit.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/um/Kconfig.rest

@@ -36,7 +36,7 @@ source "drivers/leds/Kconfig"
 
 #This is just to shut up some Kconfig warnings, so no prompt.
 config INPUT
-	bool
+	tristate
 	default n
 
 source "arch/um/Kconfig.debug"