ath9k: Set ATH_OP_HW_RESET before HW reset

When a HW reset is done, the interrupt tasklet is
disabled before ISRs are disabled in the HW. This
allows a small window where the HW can still generate
interrupts. Since the tasklet is disabled and not killed,
it is not scheduled but deferred for execution at a later
time.

This happens because ATH_OP_HW_RESET is not set when ath_reset()
is called. When the hw_reset_work workqueue is used, this
problem doesn't arise because ATH_OP_HW_RESET is set
and the ISR bails out.

Set ATH_OP_HW_RESET properly in ath_reset() to avoid
this race - all the ath_reset_internal() callers have
been converted to use ath_reset() in the previous patch.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>