staging: r8188eu: remove rtw_xmitframe_enqueue

The rtw_xmitframe_enqueue function is only one line. We can remove it and
call rtw_xmit_classifier directly.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20230123205342.229589-21-martin@kaiser.cx


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