ath11k: avoid use_after_free in ath11k_dp_rx_msdu_coalesce API

Accessing already stored first msdu data after the skb expand trigger
use_after_free, since first msdu got deleted. so do the descriptor copy
operation before the skb expand operation.

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>