Rename variable for clarity

* lisp/progmodes/verilog-mode.el (verilog-sk-define-signal):
Rename sig-re to sig-chars, to make it clear that it isn't a regexp.

lisp/progmodes/verilog-mode.el

@@ -14263,13 +14263,13 @@ and the case items."
 (defun verilog-sk-define-signal ()
   "Insert a definition of signal under point at top of module."
   (interactive "*")
-  (let* ((sig-re "a-zA-Z0-9_")
+  (let* ((sig-chars "a-zA-Z0-9_")
 	 (v1 (buffer-substring
               (save-excursion
-                (skip-chars-backward sig-re)
+                (skip-chars-backward sig-chars)
                 (point))
               (save-excursion
-                (skip-chars-forward sig-re)
+                (skip-chars-forward sig-chars)
                 (point)))))
     (if (not (member v1 verilog-keywords))
 	(save-excursion