ath10k: ath10k_pci_init_irq(): workaround for checkpatch fallthrough warning

Latest checkpatch complains about use of fall-through comment. But as this is a
switch statement just reword the comment to workaround the problem.

Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1603802288-21158-2-git-send-email-kvalo@codeaurora.org