Make sure that bind-key's override-global-mode is initially on

In 4004dde the arguments to `define-minor-mode` were changed
erroneously. Whereas the `override-global-mode` was initially defined
as `(define-minor-mode override-global-mode "..." t "")`, the two
latter arguments where changed to `:global t :lighter ""`. However,
the two original arguments corresponded to the keywords `:init-value`
and `:lighter`, respectively.

With `:init-value t` now missing, the minor mode isn't enabled by
default, and `bind-key*` appears not to work.

Copyright-paperwork-exempt: yes

lisp/use-package/bind-key.el

@@ -131,6 +131,7 @@
 
 (define-minor-mode override-global-mode
   "A minor mode so that keymap settings override other modes."
+  :init-value t
   :global t
   :lighter "")