staging: r8188eu: remove struct _io_ops

Finally struct _io_ops is unused, so remove it.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Co-developed-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
Link: https://lore.kernel.org/r/20210917071837.10926-15-fmdefrancesco@gmail.com


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