UPSTREAM: ath10k: correct target assert problem due to CE5 stuck

Correct a minor bug in the commit 0628467f ("ath10k: fix
copy engine 5 destination ring stuck") which introduced a change to fix
firmware assert that happens when ring indices of copy engine 5 are stuck
for a specific duration, problem with this fix is that it did not use
ring arithmatic. As a result,firmware asserts did not go away entirely
athough the frequency of occurrence has reduced. Using ring arithmatic
to fix the issue.

Tested on QCA9984(fw version-10.4-3.4-00082).

Fixes: 0628467f ("ath10k: fix copy engine 5 destination ring stuck)
Signed-off-by: Manikanta Pubbisetty <mpubbise@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Git-commit: 1e8f77502341035f079039c9aa9a647ebc9d881a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


Change-Id: I84b8b4c8feaea2472606601d49ac321a32153b71
Signed-off-by: Dundi Raviteja <dundi@codeaurora.org>