staging: rtl8188eu: Remove 'spinlock_t recvbuf_lock' from struct recv_buf

recvbuf_lock is initialized inside rtl8188eu_init_recv_priv() but never used.

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