staging: r8188eu: remove unnecessary rtw_free_xmitframe call

There's no need to call rtw_free_xmitframe before we dequeue the first
frame. pxmitframe is always NULL at this point, rtw_free_xmitframe will do
nothing in this case.

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/20221230180646.91008-18-martin@kaiser.cx


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