ath10k: bugfix: add USB case in ath10k_core_probe_fw

It was accidentally left out from the switch statement and target info was not
queried.

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
[kvalo@codeaurora.org: add commit log]
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>