ath10k: convert pci_alloc_consistent() to dma_alloc_coherent()

This allows to use GFP_KERNEL allocation. This
should decrease chance of allocation failure, e.g.
during firmware recovery.

Reported-By: Avery Pennarun <apenwarr@gmail.com>
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>