ath10k: htc: refactorization

Code refactorization:

Moved the code for ep 0 in ath10k_htc_rx_completion_handler
to ath10k_htc_control_rx_complete.

This eases the implementation of SDIO/mbox significantly since
the ep_rx_complete cb is invoked directly from the SDIO/mbox
hif layer.

Since the ath10k_htc_control_rx_complete already is present
(only containing a warning message) there is no reason for not
using it (instead of having a special case for ep 0 in
ath10k_htc_rx_completion_handler).

Signed-off-by: Erik Stromdahl <erik.stromdahl@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>