staging: r8188eu: remove unused field recvbuf_lock

The spinlock field recvbuf_lock in struct recv_buf is initialized but
not used. Remove it.

Signed-off-by: Abdun Nihaal <abdun.nihaal@gmail.com>
Link: https://lore.kernel.org/r/24597a0cc19fa59139bf0a77ccd11a8229d7201f.1646321515.git.abdun.nihaal@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>