ath10k: disable napi before resource cleanup to avoid "use after free"

CE buffers are cleaned up prior to napi disable and this is causing
NULL pointer dereference due to "use after free".

Disable napi before resource cleanup to avoid "use after free".

Signed-off-by: Govind Singh <govinds@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>