Fix missing :value with defcustom const :type

Fix missing :value with defcustom const :type

* lisp/calendar/calendar.el (calendar-intermonth-header)
(calendar-intermonth-text, calendar-date-style):
* lisp/calendar/diary-lib.el (diary-face-attrs):
* lisp/emacs-lisp/package.el (package-check-signature):
* lisp/erc/erc-dcc.el (erc-dcc-get-default-directory):
* lisp/gnus/gnus-art.el (gnus-auto-select-part):
* lisp/gnus/gnus-cus.el (gnus-agent-parameters):
* lisp/gnus/gnus.el (gnus-user-agent):
* lisp/mail/rmail.el (rmail-retry-ignored-headers):
* lisp/progmodes/sh-script.el (sh-indent-after-continuation):
Fix missing :value with defcustom const :type.