ath10k: fix incorrect size of dma_free_coherent in ath10k_ce_alloc_src_ring_64

sizeof(struct ce_desc) should be a copy-paste mistake
just use sizeof(struct ce_desc_64) to avoid mem leak

Fixes: b7ba83f7 ("ath10k: add support for shadow register for WNC3990")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>