kernel: add missing keyword to KERNEL_KASAN_VMALLOC

The help keyword is missing, which breaks menuconfig etc.

Fixes: cbeab2c ("kernel: add another missing KASAN symbol")

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

config/Config-kernel.in

@@ -173,6 +173,7 @@ config KERNEL_KASAN_EXTRA
 CONFIG KERNEL_KASAN_VMALLOC
 	bool "Back mappings in vmalloc space with real shadow memory"
 	depends on KERNEL_KASAN
+	help
 	  By default, the shadow region for vmalloc space is the read-only
 	  zero page. This means that KASAN cannot detect errors involving
 	  vmalloc space.