docsrc: use config instead of menuconfig

BUILD_DOCSRC should be controlled by "config" instead of "menuconfig".
I have no idea how I managed to use "menuconfig" here.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/Kconfig.debug

@@ -838,7 +838,7 @@ config FIREWIRE_OHCI_REMOTE_DMA
 
 	  If unsure, say N.
 
-menuconfig BUILD_DOCSRC
+config BUILD_DOCSRC
 	bool "Build targets in Documentation/ tree"
 	depends on HEADERS_CHECK
 	help