staging: rtl8188eu: make struct field of mlme_handler const

The strings in the uses of struct mlme_handler are constant.
Change the type of field str from 'char *' to 'const char *'.
Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Michael Straube <straube.linux@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/include/rtw_mlme_ext.h

@@ -232,7 +232,7 @@ enum SCAN_STATE {
 
 struct mlme_handler {
 	unsigned int   num;
-	char *str;
+	const char *str;
 	unsigned int (*func)(struct adapter *adapt, struct recv_frame *frame);
 };