orinoco: Move context allocation after processing the skb

ezusb_xmit() allocates a context which is leaked if
orinoco_process_xmit_skb() returns an error.

Move ezusb_alloc_ctx() after the invocation of
orinoco_process_xmit_skb() because the context is not needed so early.
ezusb_access_ltv() will cleanup the context in case of an error.

Fixes: bac6fafd ("orinoco: refactor xmit path")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201113212252.2243570-2-bigeasy@linutronix.de