staging: r8188eu: simplify dequeue_one_xmitframe

Simplify the dequeue_one_xmitframe function without changing its
behaviour. Drop the temporary variable xmitframe_plist.

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/20230123205342.229589-16-martin@kaiser.cx


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