hw/xwin: Fix const warning in winPrefsLoadPreferences()

winprefs.c:643:14: warning: assignment discards ‘const’ qualifier from pointer target type [enabled by default]

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

hw/xwin/winprefs.c

@@ -625,7 +625,7 @@ winIconIsOverride(HICON hicon)
  * If @path is NULL, use the built-in default.
  */
 static int
-winPrefsLoadPreferences(char *path)
+winPrefsLoadPreferences(const char *path)
 {
     FILE *prefFile = NULL;