init/Kconfig: fix LOCALVERSION_AUTO help text

It was never guaranteed to be exactly eight, but since commit
548b8b51 ("scripts/setlocalversion: make git describe output more
reliable"), it has been exactly 12.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

init/Kconfig

@@ -204,7 +204,7 @@ config LOCALVERSION_AUTO
 	  appended after any matching localversion* files, and after the value
 	  set in CONFIG_LOCALVERSION.
 
-	  (The actual string used here is the first eight characters produced
+	  (The actual string used here is the first 12 characters produced
 	  by running the command:
 
 	    $ git rev-parse --verify HEAD