staging: r8188eu: prevent ->Ssid overflow in rtw_wx_set_scan()

staging: r8188eu: prevent ->Ssid overflow in rtw_wx_set_scan()

This code has a check to prevent read overflow but it needs another
check to prevent writing beyond the end of the ->Ssid[] array.

Fixes: 2b42bd58b321 ("staging: r8188eu: introduce new os_dep dir for RTL8188eu driver")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Denis Efremov <denis.e.efremov@oracle.com>
Link: https://lore.kernel.org/r/20220518070052.108287-1-denis.e.efremov@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>