wacom: Fix nav label's maximum page number

The label "X of Y" pages is incorrect when multiple tablets are plugged
in, with Y being one too small. The "num_pages" variable is already
decremented if necessary on line 70, making the ternary excessive.

https://bugzilla.gnome.org/show_bug.cgi?id=668231

panels/wacom/cc-wacom-nav-button.c

@@ -88,7 +88,7 @@ cc_wacom_nav_button_update (CcWacomNavButton *nav)
 
 		text = g_strdup_printf (_("%d of %d"),
 					current_page + 1,
-					priv->ignore_first_page ? num_pages - 1 : num_pages);
+					num_pages);
 		gtk_label_set_text (GTK_LABEL (priv->label), text);
 	}
 }