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/usb/gadget/legacy/Kconfig b/drivers/usb/gadget/legacy/Kconfig
index fd48ef3..113c87e 100644
--- a/drivers/usb/gadget/legacy/Kconfig
+++ b/drivers/usb/gadget/legacy/Kconfig
@@ -40,7 +40,7 @@
 	  dynamically linked module called "g_zero".
 
 config USB_ZERO_HNPTEST
-	boolean "HNP Test Device"
+	bool "HNP Test Device"
 	depends on USB_ZERO && USB_OTG
 	help
 	  You can configure this device to enumerate using the device