ath10k: workaround boot issues with KVM/PCI-passthrough

Apparently iomap writes that unmask CE irqs aren't
propagated properly sometimes. Before failing try
to poll for the control response message as it may
have been delivered without an interrupt.

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