ath10k: re-arrange PCI init code

This patch moves irq registering after necessary
structures have been allocated and initialized.
This should prevent interrupts from causing
tasklet access invalid memory pointers.

Reported-By: Ben Greear <greearb@candelatech.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>