kconfig: use bool instead of boolean for type definition attributes

Support for keyword 'boolean' will be dropped later on.

No functional change.

Reference: http://lkml.kernel.org/r/cover.1418003065.git.cj@linux.com
Signed-off-by: Christoph Jaeger <cj@linux.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index c79b43c..9f439fa9 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -498,7 +498,7 @@
 	select SERIAL_CORE
 
 config SERIAL_MFD_HSU_CONSOLE
-	boolean "Medfile HSU serial console support"
+	bool "Medfile HSU serial console support"
 	depends on SERIAL_MFD_HSU=y
 	select SERIAL_CORE_CONSOLE