ath10k: Wait until copy complete is actually done before completing

On wcn3990 we have "per_ce_irq = true".  That makes the
ath10k_ce_interrupt_summary() function always return 0xfff. The
ath10k_ce_per_engine_service_any() function will see this and think
that _all_ copy engines have an interrupt.  Without checking, the
ath10k_ce_per_engine_service() assumes that if it's called that the
"copy complete" (cc) interrupt fired.  This combination seems bad.

Let's add a check to make sure that the "copy complete" interrupt
actually fired in ath10k_ce_per_engine_service().

This might fix a hard-to-reproduce failure where it appears that the
copy complete handlers run before the copy is really complete.
Specifically a symptom was that we were seeing this on a Qualcomm
sc7180 board:
  arm-smmu 15000000.iommu: Unhandled context fault:
  fsr=0x402, iova=0x7fdd45780, fsynr=0x30003, cbfrsynra=0xc1, cb=10

Even on platforms that don't have wcn3990 this still seems like it
would be a sane thing to do.  Specifically the current IRQ handler
comments indicate that there might be other misc interrupt sources
firing that need to be cleared.  If one of those sources was the one
that caused the IRQ handler to be called it would also be important to
double-check that the interrupt we cared about actually fired.

Tested-on: WCN3990 SNOC WLAN.HL.3.2.2-00490-QCAHLSWMTPL-1

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200609082015.1.Ife398994e5a0a6830e4d4a16306ef36e0144e7ba@changeid