orinoco: Annotate ezusb_write_ltv()

All invocation of ezusb_write_ltv() happen via ->write_ltv() and are
performed under the orinoco_lock() which disables BH.

Use ezusb_req_ctx_wait_poll() for ezusb_write_ltv() because it must not
sleep.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201113212252.2243570-8-bigeasy@linutronix.de