staging: r8188eu: remove unused members of struct xmit_buf

Remove unused members of struct xmit_buf: alloc_sz, ff_hwaddr,
dma_transfer_addr, bpending and last.

Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Ivan Safonov <insafonov@gmail.com>
Link: https://lore.kernel.org/r/20200712123821.553420-1-insafonov@gmail.com


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