staging: rtl8188eu: simplify rtw_cmd_thread's main loop

staging: rtl8188eu: simplify rtw_cmd_thread's main loop

In rtw_cmd_thread's main loop, we wait until there's a command in the
queue. To skip this wait statement in subsequent iterations, the driver
uses a label and goto instead of the actual loop. We only get back to the
initial wait if the queue is empty when we read it.

Basically, all we want to do is check if there's a command in the queue.
If yes, we process it. If not, we wait until someone enqueues a command.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210408195601.4762-12-martin@kaiser.cx
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>