cmake-mode.el: Fix byte-compilation warnings.

Auxiliary/cmake-mode.el

@@ -113,6 +113,14 @@ set the path with these commands:
 
 ;------------------------------------------------------------------------------
 
+;;
+;; Indentation increment.
+;;
+(defcustom cmake-tab-width 2
+  "Number of columns to indent cmake blocks"
+  :type 'integer
+  :group 'cmake)
+
 ;;
 ;; Line indentation function.
 ;;
@@ -225,13 +233,6 @@ the indentation.  Otherwise it retains the same position on the line"
 ;;
 (defvar cmake-mode-hook nil)
 
-;;
-;; Indentation increment.
-;;
-(defcustom cmake-tab-width 2
-  "Number of columns to indent cmake blocks"
-  :type 'integer)
-
 ;------------------------------------------------------------------------------
 
 ;; For compatibility with Emacs < 24