ath11k: cleanup reo command error code overwritten

should not overwrite the error code. No buffer available then return
invalid. For other failures return the error code of actual failure.

Signed-off-by: Govindaraj Saminathan <gsamin@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1586776872-25766-1-git-send-email-gsamin@codeaurora.org