caif-hsi: Remove wake line modification when flushing FIFO

Raising wake before flushing FIFO and lowering it after caused a
spike on AC wake that were sometimes detected and acted upon by the
modem. Fixed this by remove wake line modification when flushing FIFO.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>