ath10k: prevent hif_stop being called twice

Recently there was a bug discovered that involved
hif_stop() being called twice that ended up with a
double free_irq() call but it only manifested with
multiple MSI interrupts mapping.

Catch this kind of a problem early in driver
regardless of interrupt mapping.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>