staging: rtl8188eu: Remove 'struct list_head list' from struct recv_buf

Users of 'struct list_head list' variable e.g. rtw_enqueue_recvbuf(),
rtw_enqueue_recvbuf_to_head() and rtw_dequeue_recvbuf() are
already removed.

Signed-off-by: navin patidar <navin.patidar@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>