wlcore: clean-up clearing of WL1271_FLAG_IRQ_RUNNING

We set WL1271_FLAG_IRQ_RUNNING in the beginning of wlcore_irq(), but clear
it before interrupt handling is done in wlcore_irq_locked().

Let's move the clearing to the end of wlcore_irq() where it gets set,
and remove the old comments about hardirq. That's no longer the case as
we're using request_threaded_irq().

Note that the WL1271_FLAG_IRQ_RUNNING should never race between the
interrupt handler and wlcore_runtime_resume() as because of autosuspend
timeout we cannot enter idle between wlcore_irq_locked() and the end of
wlcore_irq().

Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: Eyal Reizer <eyalr@ti.com>
Cc: Guy Mishol <guym@ti.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>