staging: r8188eu: use lists for hwxmits

staging: r8188eu: use lists for hwxmits

struct hw_xmit's sta_list points to one of vo, vi, be or bk_pending in
struct xmit_priv. All of these are defined as struct __queue, which is a
list plus a spinlock.

For these components, the spinlock is unused, we need only the list.

This patch converts sta_list and vo, vi, be and bk_pending to struct
list_head.

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/20230123205342.229589-19-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>