Fix typo causing a void-variable error: pkg-desc

* emacs-lisp/package.el (package-installed-p): Fix typo causing
void-variable error.

lisp/ChangeLog

+2015-02-04  Tassilo Horn  <tsdh@gnu.org>
+
+	* emacs-lisp/package.el (package-installed-p): Fix typo causing
+	void-variable error.
+
 2015-02-04  Artur Malabarba  <bruce.connor.am@gmail.com>
 
 	* emacs-lisp/package.el (package-delete): Remove package from

lisp/emacs-lisp/package.el

@@ -1002,7 +1002,7 @@ should be a version list.
 If PACKAGE is a package-desc object, MIN-VERSION is ignored."
   (unless package--initialized (error "package.el is not yet initialized!"))
   (if (package-desc-p package)
-      (let ((dir (package-desc-dir pkg-desc)))
+      (let ((dir (package-desc-dir package)))
         (and (stringp dir)
              (file-exists-p dir)))
     (or